The purpose of this special issue of the Journal of Learning Disabilities is to bring to the attention of researchers and educators studies on morphology and literacy that either involve students with learning difficulties or have educational implications for teaching such students. In our introduction, we first provide background information about morphological knowledge and consider the role of morphology in literacy, focusing on findings that are relevant for instruction of students who struggle with reading and writing. Next we present an overview of the studies included in this issue, organized by current issues concerning the role of morphological knowledge in literacy. Collectively, the articles in this issue suggest that students with weaker literacy skills tend to lag behind their peers in morphological knowledge but that all students are likely to benefit from morphological instruction. Morphological interventions hold promise, especially for students who face challenges in language learning and literacy, but additional research is needed to provide a basis for informed decisions about the design of effective morphological interventions.

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This study synthesizes 79 standardized mean-change differences between control and treatment groups from 17 independent studies, investigating the effect of morphological interventions on literacy outcomes for students with literacy difficulties. Average total sample size ranged from 15 to 261 from a wide range of grade levels. Overall, morphological instruction showed a significant improvement on literacy achievement (d = 0.33). Specifically, its effect was significant on several literacy outcomes such as phonological awareness (d = 0.49), morphological awareness (d = 0.40), vocabulary (d = 0.40), reading comprehension (d = 0.24), and spelling (d = 0.20). Morphological instruction was particularly effective for children with reading, learning, or speech and language disabilities, English language learners, and struggling readers, suggesting the possibility that morphological instruction can remediate phonological processing challenges. Other moderators were also explored to explain differences in morphological intervention effects. These findings suggest students with literacy difficulties would benefit from morphological instruction.

This study examined the dimensionality of morphological knowledge. The performance of 371 seventh- and eighth-graders on seven morphological knowledge tasks was investigated using confirmatory factor analysis. Results suggested that morphological knowledge was best fit by a bifactor model with a general factor of morphological knowledge and seven specific factors, representing tasks that tap different facets of morphological knowledge. Next, structural equation modelling was used to explore links to literacy outcomes. Results indicated the general factor and the specific factor of morphological meaning processing showed significant positive associations with reading comprehension and vocabulary. Also, the specific factor of generating morphologically related words showed significant positive associations with vocabulary, while specific factors of morphological word reading and spelling processing showed small negative relationships to reading comprehension and vocabulary. Findings highlight the complexity of morphological knowledge and suggest the importance of being cognizant of the nature of morphology when designing and interpreting studies.

The current study uses a crossed random‐effects item response model to simultaneously examine both reader and word characteristics and interactions between them that predict the reading of 39 morphologically complex words for 221 middle school students. Results suggest that a reader's ability to read a root word (e.g., isolate) predicts that reader's ability to read a related derived word (e.g., isolation). After controlling for root‐word reading, results also suggest that the remaining variability in derived‐word reading can be explained by word and reader characteristics. The significant word characteristics include derived‐word frequency and root‐word frequency but not morpheme neighborhood size, average family frequency, number of morphemes, or semantic opaqueness. The significant reader characteristics include morphological awareness and vocabulary knowledge but not reading comprehension. Only phonological and orthographic‐phonological opaqueness interacted with the effect of root‐word reading, suggesting that students were less able to apply root‐word knowledge when the root word changed phonologically (with or without an orthographic change) in the larger derived word. Discussion is included regarding how findings from this study inform the development of models of word reading for adolescents.