The role of morphology in language and reading development.

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Review of Educational
http://rer.sagepub.com/content/80/2/144
The online version of this article can be found at:
DOI: 10.3102/0034654309359353
May 2010
REVIEW OF EDUCATIONAL RESEARCH 2010 80: 144 originally published online 5
Peter N. Bowers, John R. Kirby and S. Helene Deacon
Review of the Literature
The Effects of Morphological Instruction on Literacy Skills : A Systematic
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144
Review of Educational Research
June 2010, Vol. 80, No. 2, pp. 144.179
DOI: 10.3102/0034654309359353
c 2010 AERA. http://rer.aera.net
The Effects of Morphological Instruction on
Literacy Skills: A Systematic Review of the
Literature
Peter N. Bowers and John R. Kirby
Queenfs University
S. Helene Deacon
Dalhousie University
The authors reviewed all peer-reviewed studies with participants from preschool
to Grade 8 for this meta-analysis of morphological interventions.
They identified 22 applicable studies. Instructional effects (Cohenfs d) were
averaged by linguistic outcome categories (morphological sublexical, nonmorphological
sublexical, lexical, and supralexical) and comparison group
(experimental group vs. control or experimental group vs. alternative training).
The authors investigated the effects of morphological instruction (a) on
reading, spelling, vocabulary, and morphological skills, (b) for less able
readers versus undifferentiated samples, (c) for younger versus older students,
and (d) in combination with instruction of other literacy skills or in
isolation. Results indicate that (a) morphological instruction benefits learners,
(b) it brings particular benefits for less able readers, (c) it is no less
effective for younger students, and (d) it is more effective when combined
with other aspects of literacy instruction. Implications of these findings are
discussed in light of current educational practice and theory.
Keywords: meta-analysis, instructional practices, literacy, reading, elementary
schools.
Our purpose in this article is to provide a systematic review of the evidence
about the effects of instruction about the morphological structure of words on literacy
learning. Morphology is the conventional system by which the smallest units
of meaning, called morphemes (bases, prefixes, and suffixes), combine to form
complex words.1 For example, the word unhelpful has three morphemes that can
be represented orally, /.n/ + /hƒÃlp/ + /f.l/, or in writing, <un-> + <help> + <-ful>.
The English orthography is considered to be morphophonological (Chomsky &
Halle, 1968; Venezky, 1967, 1970, 1999), in that both units of meaning and of
sound are represented in print. Morphology has received far less attention in literacy
research than has phonology (National Reading Panel, 2000). As we see in
the review that follows, there is growing evidence of the role of morphological
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Morphological Instruction
145
knowledge in literacy development (Carlisle, 2003; Deacon & Kirby, 2004; Nunes,
Bryant, & Bindman, 1997; Roman, Kirby, Parrila, Wade-Woolley, & Deacon,
2009).
Morphological knowledge is referred to in various ways in the literature,
including as morphological awareness and morphological processing.
Morphological awareness has a specific meaning, referring to gawareness of morphemic
structures of words and the ability to reflect on and manipulate that structureh
(Carlisle, 1995, p. 194). Morphological processing on the other hand can
include less conscious or implicit processing of morphological information (e.g.,
Deacon, Parrila, & Kirby, 2008). For the purposes of this review, because it was
not always clear what the participants were learning, we use the more general term
morphological knowledge.
Morphological knowledge has the potential to affect literacy skills in at least
three ways, through word recognition, comprehension, and motivation. A great
deal is known about the factors supporting word recognition: These include phonological
awareness, rapid automatized naming, orthographic processing, and
vocabulary knowledge (for a review, see National Reading Panel, 2000).
Morphological knowledge is a further factor supporting efficient and accurate
word recognition (Carlisle, 2003). For example, morphemic boundaries affect the
pronunciation of letter sequences: ea is pronounced as one phoneme in reach
because it occurs in one morpheme but as two phonemes in react because the two
letters are in different morphemes. The relationship between morphological
knowledge and word reading has been shown to be independent of the other factors
mentioned above (Deacon & Kirby, 2004; Roman et al., 2009). Morphological
knowledge may also contribute to reading comprehension, through improved
word recognition, but also by helping readers understand the meanings or syntactic
roles of unknown words (Carlisle, 2003). A number of the authors of the intervention
studies reviewed here commented that morphological instruction may
contribute to literacy by increasing motivation to investigate words (e.g., Berninger
et al., 2003; Bowers & Kirby, in press; Tomesen & Aarnoutse, 1998). We found no
studies that included outcome measures of motivation, so this interpretation is still
speculative.
Given the increasing evidence of the relationship between morphological
awareness and reading outcomes (e.g., Carlisle, 2003), there is a parallel increase
in interest in teaching children about morphology. By its nature morphological
instruction addresses sublexical features of a language. The ultimate goal of this
instruction, however, is not for children to learn about morphemes. Rather, it is
hoped that explicit morphological instruction will increase understanding about
oral and written features of morphology at the sublexical level that, in turn, will
influence literacy skills at the lexical level (e.g., word reading, spelling, and vocabulary)
and the supralexical level (e.g., reading comprehension). For sublexical
morphological instruction to result in literacy gains at higher linguistic layers,
there must be some transfer beyond that sublexical content. Presumably this transfer
would occur through improved word recognition, which in turn might facilitate
text comprehension. It can be expected then that any gains found for lexical measures
would be less than gains found for morphological sublexical tasks. Similarly,
it may be that increased knowledge of morphemes as meaning cues for words
could affect reading comprehension, the supralexical layer. Transfer to reading
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Bowers et al.
146
comprehension may be less immediate and weaker than that found for the lexical
layer and may require the integration of morphological knowledge with other literacy
skills.
The merits of new instructional content cannot be effectively investigated in
isolation from questions about how that content is taught and the individual differences
among those who receive the instruction. Any benefits of morphological
instruction may differ greatly based on a variety of factors. Developmental issues
such as the learnerfs age and language ability at the point of instruction may have
instructional consequences. Instructional design questions include the ideal length
of interventions and the optimal manner of presentation of morphological content.
These instructional questions also provide structure to our investigation of morphological
intervention studies.
Importance of Morphological Knowledge in Reading Outcomes
Before reviewing the studies of morphological instruction, it is helpful to
briefly review evidence for the correlation between morphological knowledge and
literacy in students who have not received special morphological instruction.
Morphological knowledge (assessed in the absence of specific instruction) has
been found to predict unique variance in sublexical tasks such as pseudo-word
reading after controlling for factors including phonological awareness, orthographic
processing, and naming speed (e.g., Deacon & Kirby, 2004; Fowler &
Liberman, 1995; Roman et al., 2009). An influence of morphological knowledge
on lexical tasks has been shown in studies of word reading accuracy (e.g., Carlisle,
1995, 2000; Carlisle & Katz, 2006; Elbro & Arnbak, 1996; Fowler & Liberman,
1995; Leong, 1989; Roman et al., 2009; Singson, Mahony, & Mann, 2000). Also
at the lexical layer, morphological knowledge has been shown to predict unique
variance in vocabulary knowledge (Bertram, Laine, & Virkkala, 2000; Carlisle,
2007; Mahony, Singson, & Mann, 2000; Wysocki & Jenkins, 1987) and spelling
(e.g., Deacon, Kirby, & Bell-Casselman, 2009). Finally, evidence at the supralexical
level can be found in research showing a unique contribution of morphology
to reading comprehension after controlling for other variables associated with
reading (e.g., Carlisle, 1995, 2000; Deacon & Kirby, 2004; Elbro & Arnbak, 1996).
Although the correlational or predictive studies offer strong support for the role of
morphological knowledge in literacy development, correlational studies can never
completely answer the question of causation.
Developmental Trends and the Timing of Instruction
There is some suggestion of changes in the role of morphological knowledge
for literacy skills in different age groups. Early research established that children
as young as 4 years had morphological knowledge (e.g., Berko, 1958). Evidence
for morphological cues influencing spelling has been shown for 5- and 6-year-old
children (Deacon & Bryant, 2006; Kemp, 2006; Treiman, Cassar, & Zukowski,
1994). Carlisle and Stone (2005) found that children aged 7 to 10 years made
use of morphological structure in reading derived words (also see Deacon, Whalen,
& Kirby, 2010). There is some suggestion that the role of morphological knowledge
in reading increases with age whereas that of phonological awareness
decreases (Singson et al., 2000), but that does not appear in all analyses in all studies
(e.g., Deacon & Kirby, 2004; Roman et al., 2009). Certainly, an increase in the
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Morphological Instruction
147
importance of morphological knowledge is the prediction of some prominent models
of literacy development (e.g., Ehri, 1995, 1997; Ehri & McCormick, 1998);
children are expected to become more fluent readers later in reading development
as they increasingly use commonly recurring letter patterns (e.g., .ight and .ed) as
units. Notably, these units include morphemes. The question of the developmental
pattern of the contributions of morphological knowledge to reading outcomes
clearly has substantial empirical and theoretical implications.
Accordingly, the most effective point at which to introduce this content to classroom
instruction remains an important unresolved question. Adams (1990) recommended
avoiding explicit morphological instruction until upper elementary years.
More recently, researchers have called for early instruction about morphology
along with other oral and written features of language (e.g., Carlisle & Stone,
2005; Henry, 2003; Nunes & Bryant, 2006). Results from intervention studies are
needed to shed light on when this instruction is most effective.
Differential Effects Associated With Reading Ability
The role morphological knowledge plays for more and less able readers is
another important question. A well-established source of difficulty for struggling
readers is a phonological processing deficit (National Reading Panel, 2000). A
number of researchers have suggested that morphological knowledge may represent
a particular advantage for struggling readers (e.g., Carlisle, Stone, & Katz,
2001; Casalis, Cole, & Sopo, 2004; Elbro & Arnbak, 1996). As an example,
Carlisle et al. (2001) found that both poor and average readers were better able to
read morphologically transparent words than shift words (transparent words are
those in which the pronunciation of the base is the same after adding affixes,
whereas shift words are those in which the basefs pronunciation changes). Carlisle
et al. concluded that both poor and average readers must draw on morphological
knowledge when they are reading. A more detailed picture comes from Casalis et
al. (2004). They found that dyslexics were behind reading-age controls in morphemic
segmentation but that the two groups performed equally in a morphological
sentence completion task and dyslexics in fact outperformed the reading-age controls
in a morphological production task. They concluded that dyslexics might take
advantage of morphemes in processing, particularly given that these are typically
larger units of sound that are connected to meaning. Introducing explicit morphological
instruction may build on a relative strength for dyslexic learners (Deacon
et al., 2008; Elbro & Arnbak, 1996).
Rationale for Studying Morphological Instruction
Typical classroom instruction includes very little, if any, systematic and sustained
attention to the morphological structure of words (Henry, 2003; Moats, in
press; Nunes & Bryant, 2006). Therefore, virtually all the findings outlined in the
preceding sections are based on uninstructed morphological knowledge. Only
examination of evidence from morphological interventions can shed light on the
causal role of morphological knowledge and whether the existing research accurately
represents the role morphology plays in literacy development.
The distinction between taught and untaught morphological knowledge may
have special relevance for some of the questions addressed in the preceding sections.
If uninstructed morphological knowledge provides some struggling readers
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Bowers et al.
148
with a compensation strategy, as suggested by Casalis et al. (2004), deliberate
morphological instruction may help them harness this strategy more effectively.
Deliberate morphological instruction may create knowledge that is different from
the untaught knowledge examined in existing correlational or predictive studies.
Deliberate instruction should lead to more accurate and quicker learning and more
explicit knowledge. If morphological instruction were introduced early in literacy
learning, morphological knowledge would have time to become consolidated and
have more opportunities to contribute to literacy learning.
Intervention studies are necessary to investigate the causal links between morphological
knowledge and literacy development, just as studies such as Bradley
and Bryantfs (1983) were needed to establish a causal link between phonological
awareness and later reading ability. The predictive or correlational studies are
important but fail to address the directionality of influence between morphological
knowledge and literacy skills. It may be that morphological knowledge builds
literacy skills or that developing literacy skills build morphological knowledge or
that there is some mutually supportive relationship. Evidence from morphological
interventions is needed to determine whether an increase in morphological knowledge
will influence the development of literacy skills. Also, as we revisit in more
detail in the discussion, the question of whether morphological instruction is helpful
for younger and/or less able readers has clear implications for current models
of reading development (e.g., Ehri, 1995).
Current Morphological Instruction Research
A small but growing body of research has investigated the effects of morphological
instruction on reading (e.g., Abbott & Berninger, 1999; Berninger et al.,
2003; Berninger et al., 2008), spelling (e.g., Nunes, Bryant, & Olsson, 2003;
Robinson & Hesse, 1981), and vocabulary (Baumann, Edwards, Boland, Olejnik,
& Kamefenui, 2003; Baumann et al., 2002; Bowers & Kirby, in press). The metaanalysis
described here synthesizes results from morphological interventions that
have examined the effect of instruction both with participants identified with reading
difficulties (e.g., Arnbak & Elbro, 2000; Tyler, Lewis, Haskill, & Tolbert,
2003) and spelling difficulties (e.g., Kirk & Gillon, 2009) and with undifferentiated
participants (e.g., Baumann et al., 2002; Baumann et al., 2003; Bowers &
Kirby, 2006, in press). We investigate results from instructional studies with age
groups from preschool (e.g., Lyster, 1998, 2002) to upper elementary (e.g.,
Robinson & Hesse, 1981) and across a variety of languages (English, Danish,
Dutch, and Norwegian). A meta-analysis will allow patterns to be seen on a larger
scale than is possible in separate studies and will to some extent overcome limitations
because of sample size, instructional methods, and variable selection.
Reed (2008) published the only quantitative synthesis of morphological interventions
that we have been able to identify. Her study investigated morphological
intervention studies conducted in English between 1986 and 2006 with students
from kindergarten to Grade 12. Reed identified seven studies that met her inclusion
criteria and provided a descriptive account of the effect sizes for all outcome
measures.
In her sample, three studies focused on word identification, three on
vocabulary, and one on spelling. Reed reported a wide range in effect sizes and
concluded that stronger effects were associated with instruction focused on root
(base) words compared to affixes alone. Three studies from two publications in her
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Morphological Instruction
149
review (Abbott & Berninger, 1999; Vadasy, Sanders, & Payton, 2006) specifically
selected low achieving readers. Reed reported medium effect sizes on reading and
reading-related outcomes from these studies and found these effects to be larger in
general than those for the other intervention studies. She concluded that morphology
instruction should be tailored to studentsf developmental age and that it should
include instruction about root (base) words.
Purpose of the Current Study
Our study is designed to provide a comprehensive systematic review of available
data on the impact of morphological instruction on literacy outcomes. To do
so, we included a wide search range (expanding on that offered in Reed, 2008). We
included studies reported prior to 1986 and unpublished studies presented at peerreviewed
scientific conferences. To identify all relevant studies, we included studies
even if they did not explicitly state they were investigating morphology (unlike
Reed), as long as the focus on morphology was clear from the description of the
studiesf methods. We included studies that took place in other alphabetic orthographies
(as it turned out, there were studies in Danish, Dutch, and Norwegian),
extending Reedfs exclusive focus on English.
Interpreting results from interventions across languages should be done cautiously
because languages differ in terms of oral and written features. One criterion
the literature uses to distinguish alphabetic languages is the complexity of grapheme
to phoneme correspondences. Languages with consistent grapheme.phoneme
correspondences are considered shallow. Languages in which the grapheme.phoneme
correspondences are complex and inconsistent are labeled deep. Although
English is seen as deep for both spelling and reading, Danish, Dutch, and
Norwegian are seen as moderate on these dimensions (e.g., Borgwaldt, Hellwig,
& de Groot, 2004, 2005; Bosman, Vonk, & van Zwam, 2006; Seymour, Aro, &
Erskine, 2003; Stone, Vanhoy, & Van Orden, 1997). Although there are too few
studies in languages other than English to compare languages statistically, we
judged it more advantageous to include all these languages in our review to provide
a wider sample of studies for this early assessment of morphological interventions.
As noted regarding study selection criteria, we did limit the studies to those
conducted in alphabetic orthographies.
Our study employed a design to facilitate synthesis of this wide variety of data
according to three linguistic layers. Outcomes for all studies were coded as sublexical,
lexical, or supralexical in nature. This categorization system (which is
described in more detail in the method section) allowed us to draw a more finegrained
picture of the effects of instruction. Our design allows us to investigate the
degree to which sublexical instruction transfers up to lexical and supralexical measures.
We expect high variability within and between these categories because of
the application of different treatments to different students and a wide variety of
outcomes. Nevertheless, analyzing effect sizes by these linguistic categories
allows for a principled synthesis of results across a variety of studies to investigate
pertinent
theoretical and practical questions. To investigate ability and age effects,
we categorize studies on those characteristics.
If morphological instruction does transfer from the sublexical to the lexical and
supralexical levels, this transfer is likely to be facilitated by instructional methods
that integrate morphological instruction with other aspects of literacy instruction
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Bowers et al.
150
(cf. Salomon & Perkins, 1989). This type of integrated instruction, as opposed to
that which presents morphological knowledge in a more isolated fashion, should
provide more opportunities for guided application of morphological knowledge at
the lexical and supralexical levels. It is also possible that greater application at the
higher levels will work backward to strengthen sublexical skills. To investigate
this, we also categorize the studies with respect to this characteristic.
In summary, this systematic review assesses the evidence for literacy and morphological
gains for elementary students (preschool through Grade 8) through
explicit instruction about morphology. Our research questions are the following:
(a) What are the effects of morphological instruction for sublexical, lexical, and
supralexical measures of reading, spelling, vocabulary, and morphological skills?
(b) Is the effect of morphological instruction different for less able than undifferentiated
children? (c) Does the effect of morphological intervention differ when
conducted with older versus younger students? and (d) Is morphological instruction
more effective when taught in isolation or integrated with other literacy
knowledge and skills?
Method
Study Selection
To identify the relevant studies, the EBSCO Research Complete, PsycINFO,
and WorldCat electronic databases were searched with the following descriptors:
morpholog*, morphem*, interven*, teach*, train*, instruct*, vocabulary, spell*,
read*, base*, root*, prefix*, suffix*, affix*, litera*, dyslex*. More than 1,000
abstracts were identified by December 7, 2009. To be included in the analysis,
studies needed to meet all the following criteria:
1. Published in English, reporting on research carried out in an alphabetic
orthography
2. Investigated instruction with elementary school students (preschool to
Grade 8)
3. Investigated instruction about any element of oral or written morphology
(including prefixes, suffixes, bases or roots, compounds, derivations, and
inflections; studies did not need to mention morphology explicitly, as long
as the role of morphology was clear in the description of the intervention)
4. At least one third of the instruction was focused on morphology, based on
the intervention description
5. Reported literacy outcome measures (including morphological measures)
with means and standard deviations for comparison
6. Used either an experimental and control or comparison group or a training
group with pre- and posttests using measures that could be compared to established
norms (no studies were identified that used a pretest.posttest design
without a comparison group, so this last criterion was not implemented)
Once studies meeting these criteria were identified, experts in the field were contacted
to inquire whether they could identify additional relevant published or
unpublished studies. Reference lists from identified studies were examined for still
more potentially relevant studies. In all, 22 studies met the inclusion criteria; these
are identified with an asterisk in the reference list.
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151
Coding the Studies and Outcome Variables
Studies and outcome variables were coded for characteristics of type of linguistic
outcome measure, participants, and instructional design. We describe each in
turn.
Coding outcomes by linguistic layer. An overarching system of coding outcome
measures was designed to facilitate the synthesis of a wide array of outcomes from
the 22 studies along the dimensions relevant to our research questions. Sublexical
outcomes were defined as tasks that require students to process sublexical features
and that were scored on the basis of sublexical features, even if the stimulus and/
or responses were at the lexical level. Sublexical tasks were further subdivided into
morphological sublexical tasks and nonmorphological sublexical tasks.
Morphological sublexical tasks included oral tasks such as morphological analogy
(walk : walked :: shake :______ (shook); Nunes et al., 1997) or written morphological
tasks in which students select words linked by the base to a cue word (e.g.,
identifying which of the following words ghave a real connectionh to the cue word
create: creative, cream, creature, ate, recreation, crease; Bowers & Kirby, 2006).
Nonmorphological sublexical tasks included phonological awareness, syllable
segmentation, pseudo-word reading, and rhyme recognition.
Lexical outcomes included tasks that target linguistic processing at the word level,
even though participants must process sublexical features to complete them. Lexical
outcome tasks include vocabulary, word reading accuracy or efficiency, spelling, and
word-level orthographic processing tasks such as those in which students choose the
correct spelling of two phonologically plausible options (e.g., rain or rane). Lexical
outcomes were further coded as measures of reading, spelling, or vocabulary.
Supralexical outcomes included tasks that required oral or written processing
beyond the word level. Examples include reading comprehension tasks, syntactic
awareness, and listening comprehension.
Coding of participant characteristics. Studies were first coded to indicate whether
they investigated less able or undifferentiated readers. The authorsf formal identification
of participants (e.g., those with dyslexia or specific language impairment)
or informal designations such as gstudents achieving below expected levelsh
resulted in the coding of gless able.h Samples that failed to select for different ability
levels were coded as gundifferentiated.h Studies were then coded according to
participantsf grade level, either from preschool to Grade 2 or from Grade 3 to
Grade 8. This division is consistent with models of reading development (Ehri,
1995, 1997; Ehri & McCormick, 1998) cited earlier.
Coding of instruction and study characteristics. To investigate our question about
instructional design, each study was coded as using either integrated or isolated
morphological instruction. Studies that combined morphological instruction with
instruction about literacy strategies and knowledge were coded integrated.
Interventions that solely focused on morphological content were coded isolated.
For descriptive purposes, we also coded various aspects of the instruction.
Studies were also coded on two study characteristics to aid analysis of the
reported effects: (a) experimental versus quasiexperimental.that is, random or
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Bowers et al.
152
not random assignment of participants to conditions.and (b) comparison group
type.whether treatment groups were compared to untrained control groups
(termed E vs. C comparisons) or to comparison groups which received alternative
treatment (E vs. AT). None of the alternative treatments included any explicit morphological
instruction.
Effect Size as an Index of Treatment Efficiency Across Studies
The effect size statistic used in this study is Cohenfs d, which is calculated as
the difference between the mean posttest score of the treatment group and that of
the comparison group, divided by the pooled standard deviation. An effect size of
1.0 represents a difference of 1 standard deviation between the treatment and comparison
groups. Cohen (1988) provided general benchmarks for effect sizes of 0.2
as small, 0.5 as medium, and 0.8 as large but emphasized that this guideline is
subject to judgment. Thompson (2006) explained that depending on the potential
consequences of a given outcome, small effect sizes could be of large practical
importance, just as large effect sizes could be of little practical significance.
One concern with meta-analyses is that there may exist unpublished studies
with null findings that, if they were included in the calculation of the overall effect
size, would reduce it below the level at which it would be meaningful or useful (the
so-called gfile drawerh problem). Therefore, we indicate in the analyses the number
of null effects (i.e., d = 0.0) that would be required to reduce the effects found
below d = 0.2 (Hunter & Schmidt, 2004). We chose the 0.2 criterion on the basis
of Cohenfs (1988) benchmarks.
Results
Sample Characteristics
Table 1 presents basic information about each study analyzed. This table is
organized by the sample populations studied rather than by publication. Some
publications reported on more than one study (Hurry et al., 2005; Tyler et al., 2003;
Vadasy et al., 2006), and some samples or interventions were used for more than
one study (Bowers & Kirby, 2006, in press; Lyster, 1998, 2002). Table 1 also provides
the identification numbers assigned to each study as a shorthand when discussing
groups of studies. A total of