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Perfetti (2007) also argued that lexical quality is important for reading compre-
hension (supralexical performance). He suggested that the source of the ability to
efficiently retrieve the words needed during reading is the integrated orthographic,
phonological, grammatical, and semantic word knowledge that the reader has for
a given word—the quality of that word’s lexical representation. If morphological
instruction increases lexical quality, those stronger mental representations could
improve reading comprehension by (a) increasing efficiency of word identifica-
tion, thereby reducing the cognitive load needed for processing and integrating
connected text, and (b) providing the reader with easier access to semantic infor-
mation associated with that word. The reading comprehension gains from morpho-
logical instruction should be less robust than the lexical gains, at least in the short
term, but if morphological instruction does improve lexical quality, it should
become apparent in reading comprehension measures, and that is what we found.
The instruction investigated in this review addresses aspects of word knowl-
edge that directly bear on efficient processing of words and meanings during read-
ing. Perfetti (2007) stated, “Underlying efficient processes are knowledge
components; knowledge about word forms (grammatical class, spellings and pro-
nunciations) and meanings. Add effective practice (reading experience) of these
knowledge components, and the result is efficiency: the rapid, low-resource
retrieval of a word identity” (p. 359). The interventions reviewed in this study used
instruction that explicitly targeted knowledge about oral and written morphologi-
cal features of words. Morphemes are characterized by consistent spelling patterns
but are also associated with pronunciations and meanings, and they may also mark
grammatical cues. Explicit morphological instruction offers teachers a way of
directly targeting the development of lexical quality. Such cognitive processing
itself may function to strengthen mental representations and decrease cognitive
load (e.g., Schnotz & Kürschner, 2007; Sweller, 1988) in reading.
However, explicit morphological instruction is not required for morphological
knowledge to develop and play a role in developing lexical quality. This is dem-
onstrated in the correlational or predictive studies we reviewed briefly at the begin-
ning of this article (for a more extensive review, see, e.g., Carlisle, 2003). In the
absence of explicit instruction in morphology, children develop considerable com-
petence in it, and this competence is related to success in literacy. There is also
evidence that simple exposure to the consistent underlying structures that integrate
morphological families improves the quality of our lexical representations. Nagy,
Anderson, Schommer, Scott, and Stallman (1989) found that adults read words
from larger morphological families more fluently than words from small families
and cited this as evidence that words are processed through morphological rela-
tionships, not as separate entities (for similar results with children, see Carlisle &
Katz, 2006). Citing the work of Taft and colleagues with adult readers (e.g., Taft,
2003; Taft & Kougious, 2004; Taft & Zhu, 1995), Carlisle and Stone (2005)
described the role of uninstructed experiences with morphology on lexical
representations by concluding that “frequent encounters with a base word (by itself
or combined with affixes in words) reinforce the mental representation of the mor-
phemes in those words, and access to memory for the morphemes speeds identifi-
cation of words containing those morphemes” (p. 431).
Untaught morphological knowledge may also lie behind the relative weakness
of the instructional effects beyond the sublexical level. Some children in the
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control or alternative treatment groups may have developed enough morphological
knowledge to support their lexical and supralexical processing, so that they per-
form as well as children who received explicit morphological instruction at these
levels. This may also be related to the stronger effects we found for less able read-
ers (see the next section). Morphological instruction that was sustained and inte-
grated with other literacy instruction over an extensive period of time may show
greater transfer.
Reading Ability Effects
In response to our second research question, we found that the effects of mor-
phological instruction were stronger on average in groups of less able readers than
in more broadly based samples. Reed (2008) came to the same conclusion from a
smaller set of studies. We see four plausible explanations for this pattern. First, the
more able readers may already have known at least implicitly some of the morpho-
logical content being taught and so would not differ as much from the comparison
groups as the poor readers, who initially were likely to know little of the content
being taught. Less able readers may need more explicit instruction. Second, the
studies involving less able learners generally used small groups rather than class-
sized groups in their instruction. Although smaller group sizes are representative
of remedial instruction, it is possible that this approach would also have been more
successful with the more able learners.
The third interpretation is that morphology is a cognitive domain that is a rela-
tive strength for less able readers. A common characteristic of struggling readers
is weak phonological awareness (e.g., National Reading Panel, 2000). Casalis et
al. (2004) suggested that dyslexics may use (untaught) morphological knowledge
as a compensatory strategy and that introducing explicit morphological instruction
could build on a relative strength for dyslexic learners; the same may be true for
other less able readers. A phonological processing deficit may be less of a hin-
drance to developing higher quality lexical representations if explicit instruction
in morphological structure builds up an integrated lexical representation of ortho-
graphic patterns and meaning cues to which phonological associations can be
linked. Making the written morphological structures more salient could scaffold
more effective use of phonological knowledge for less able readers. In effect,
explicit instruction about sublexical morphological structures and how they link to
orthographic, semantic, phonological, and grammatical cues may activate the con-
stituent binding quality offered by morphology (see the earlier discussion of
Perfetti’s, 2007, lexical quality hypothesis). Phonological processing deficits may
be less of an impediment when students are explicitly shown how phonological
structures link to linguistic structures for which these students have no processing
deficit.
Findings from one intervention in our review illustrate how morphology might
act as a binding agent of multiple features for less able readers. Arnbak and Elbro’s
(2000) intervention with Danish dyslexic students was restricted to oral instruc-
tion, and yet their strongest results were for measures of spelling, and this was
despite the fact that the control groups had more practice with written words in
their typical remedial instruction. They hypothesized that awareness of morphemic
units in words facilitated the segmenting of complex words into linguistic units
they knew how to spell and that this process may have also eased the load on
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verbal working memory. Morphological instruction may have facilitated the abil-
ity to maintain meaningful units of words (morphemes) in working memory while
spelling, which may be another consequence of increased binding.
The fourth explanation of why morphological instruction was more effective
for less able readers is through providing increased motivation to work with words.
A number of authors of the studies in this sample commented on the enthusiasm
children showed during morphological instruction; increased motivation and
improved literacy skills may mutually support each other (e.g., Berninger et al.,
2003; Bowers & Kirby, in press; Tomesen & Aarnoutse, 1998). Without measures
for motivation, however, this explanation remains speculative. The ability and
motivation to explore language independently, “word consciousness,” is a fre-
quently emphasized goal of vocabulary instruction (Graves, 2006; Scott & Nagy,
2004; Stahl & Nagy, 2006). Less able readers are likely to have had more frustrat-
ing experiences in school trying to understand how written words work. Introducing
morphology as an organized system that links words even when pronunciation
shifts appear irregular (e.g., heal/health, sign/signal) may motivate struggling stu-
dents to study words more closely. Studying morphological families of words also
has the advantage of exposing struggling older students to advanced, complex
vocabulary with the support of connected words they do know. For example,
studying the sign family can be used to introduce words such as design, designate,
insignia, significantly, and assignment. Studying the structure and meaning con-
nections in these words builds lexical representations in a way that does not require
struggling readers to process long passages of text.
Further research will be required to select among these explanations for the
greater effectiveness of morphological instruction with less able readers. It is also
possible that more able readers would show increased benefit from morphological
instruction if it were tailored to their strengths.
Grade-Level Effects
The answer to our third research question was that morphological instruction
was at least as effective for students in the early stages of formal literacy instruc-
tion as it was for students in later grades (see Table 6). These findings challenge
the assertion by Adams (1990) that “teaching beginning or less skilled readers
about them [roots and suffixes of morphologically complex words] may be a mis-
take” (p. 152). Evidence that morphological instruction brings benefits to younger
students and that this instruction brings special benefits to less able students could
have important practical implications. With a foundation of morphological knowl-
edge gained with the support of instruction from the start, it is possible many
students who fail in response to typical instruction could achieve much stronger
success.
A striking example of the potential of early and sustained morphological
instruction comes from Lyster’s (1998, 2002) study with Norwegian children. She
investigated the effects of morphological and phonological interventions com-
pared to a control group with students prior to school entry. She found a very large
effect of morphological instruction (d = 1.88) on a word reading measure 6 months
after the intervention stopped. The phonological intervention group showed a
gain of d = 0.82 on this same measure. Compared to controls, she also found a
significant difference for the morphological group (effect sizes not provided) on
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an orthographic coding task in Grades 2 and 3. Although there were relatively few
intervention studies with young children, the magnitude of the possible effects
suggests that further studies be conducted.
Effects of Methods of Instruction
The fourth research question asked whether instruction that integrated mor-
phology with other aspects of literacy instruction would differ in its effects from
isolated instruction. For the majority of outcome comparisons, including those
with alternative treatments, integrated instruction was more effective than isolated
instruction, and in the other cases the effects were similar (see Table 7). Integrated
instruction should facilitate construction of lexical representations in which pho-
nological, orthographic, grammatical, and semantic information is linked to mor-
phological information. By generating richer lexical representations, instruction
that integrates morphological and other linguistic features should facilitate lexical
access and thus enhance the binding role of morphology, more so than would be
accomplished by isolated instruction.
Vocabulary is one of the most obvious other areas of literacy instruction to
integrate with morphological instruction. Despite the importance of vocabulary
instruction cited by National Reading Panel (2000), there is a growing recognition
that vocabulary instruction has received insufficient attention in classroom instruc-
tion and literacy research (Beck et al., 2002; Biemiller & Boote, 2006). Because
morphemes, when encoded in print, are fundamentally orthographic representa-
tions of sublexical and lexical meaning units that occur in multiple words, written
morphological instruction may provide a generative component within vocabulary
instruction, supporting transfer to the learning of new words (Bowers & Kirby, in
press).
The final point to be made about methods of instruction concerns the problem-
solving approach adopted in four of the studies reviewed here (Baumann et al.,
2003; Berninger et al., 2003; Bowers & Kirby, 2006, in press; Tomesen &
Aarnoutse, 1998). Each of these studies used the theme of “detectives” to frame
their instruction, designed to enhance student motivation. Although not one of our
research questions, the inclusion of a problem-solving approach may be a critical
feature in obtaining transfer beyond the morphological sublexical level. Although
there were not enough appropriate studies to assess this possibility quantitatively,
the problem-solving approach appears to be worth further investigation. This
instructional strategy may have its effect in part by increasing students’ focus on
the working of words while fostering the deeper processing associated with more
effective long-term learning. Employing problem-solving tasks about spelling–
meaning connections (Templeton, 2004) should also develop the constituent bind-
ing feature in Perfetti’s (2007) lexical quality hypothesis by targeting the juncture
of semantics, orthography, and phonology during an engaging task.
Limitations, Future Directions, and Conclusions
Several limitations deserve noting. First, this review was limited by the number
of studies available. If there had been more studies in the literature, further research
questions could have been addressed and the variability we observed in the effects
may have been reduced. There is a need for more fine-grained studies of morpho-
logical instruction, to determine how to maximize its effects. We have presented a
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