The Developmental Similarity (Continuity) Construct: A Commentary

Method

The selection of articles for this manuscript is based on a methodology labeled a professional review [2,3]. Professional reviews are typically attempts to provide and clarify an overall conceptual picture for a broad topic such as language or literacy development. Authors select and synthesize a representative sample of publications to support their arguments.

As is the case for any type of literature review, some limitations should be mentioned. One limitation is that such a review can be biased because it is based on the selection and interpretation of research by the author. Other authors may render different interpretations and question the selection of sources. Another limitation of the present review is that there was no attempt to evaluate the quality indicators/technical merits of the selected works. Nevertheless, it is argued that the present review should facilitate and guide future explorations, necessary for improving the reading skills of children who are struggling readers or who have formally diagnosed disabilities.

Background of the developmental similarity (continuity) hypothesis

For much of the 20th century, there was a prevailing assumption that the developmental trajectory of children with disabilities was radically different from that of typical learners without disabilities [1,4]. This assumption seemed to support, in part, the development and implementation of “separate curricula” and specialized, individualized instructional methods for these children. In addition, the assumption tended to justify their placement in separate education programs such as special schools and institutions or self-contained classrooms in public schools.

Cracks in the assumption began to appear before the passage of PL 94-142 in 1975 and its subsequent amendments [1]. There was evidence that children with disabilities can benefit from being in classrooms with peers without disabilities [5]. Additional support for the inclusion of these children in general education classrooms was provided by scholars who argued that their acquisition of knowledge is developmentally similar to that of typical children [4]. In short, these children should have access to and will benefit substantially by being exposed to the same general education curricula as typical children without disabilities.

Strong early support for the similarity hypothesis can be seen in the work of Lenneberg [6,7] for language development and in the work of Stanovich for reading development [8-10]. There are several other scholars who have provided evidence for this hypothesis, for example, Adams, Goswami [11,12], and Perfetti [13]. The works of Lenneberg and Stanovich, discussed in the subsequent sections, are selected here as exemplars. Specifically, they provided the impetus, in my view, for the development of reading similarity models and have influenced my own Qualitative Similarity Hypothesis for d/Deaf and hard-of-hearing children and adolescents [14,15,].

The work of lenneberg

[6] examined the language acquisition processes of children with intellectual/cognitive disabilities. Interestingly, Lenneberg attempted to clarify the biological foundations of language acquisition with his participants. He focused on examining the critical period hypothesis (i.e., optimal period for language development) and argued that language was driven by biological maturation processes rather than solely by general intelligence.

This led to an ingenious method of matching groups of children on mental age, rather than chronological age. There were (and still are) concerns with the determination of mental age via the use of intelligence tests or even Piagetian tasks [16]. Nevertheless, Lenneberg was able to demonstrate that the language acquisition of children with intellectual/cognitive disability was developmentally/qualitatively similar (i.e., manner, process), albeit quantitatively delayed (i.e., slower rate, amount) with respect to mental age. He also asserted that children with cognitive impairments can acquire complex grammar and other language variables with adequate language input during the critical period (i.e., typically up to puberty). These findings have been corroborated by more recent research, including for children who are struggling language and literacy learners as well as those with intellectual/cognitive disabilities [17,18].

The work of stanovich

Stanovich’s developmental lag hypothesis focused on the early acquisition of reading skills before the third grade (in the USA) [8,9]. This hypothesis was an attempt to provide explanations for reading difficulties and to ascertain developmental trajectories in struggling readers, particularly those with “garden-variety” reading disabilities (i.e., non-dyslexic). In essence, Stanovich proposed a critical or optimal period for the development of beginning reading skills—essentially up to about the third-grade level. Because reading materials become exponentially more difficult and complex after the third grade, Stanovich argued that children need to learn to read by the third-grade level (i.e., reach a level of competence). Otherwise, they will not be able to read to learn, and they will continue to fall behind. This hypothesis provided a broader framework for Stanovich’s Matthew Effects—which states that good readers continue to develop higher levels of literacy whereas poor or struggling readers fall further behind grade level, resembling a spiraling downward trend.

Using reading-level matched designs (i.e., matched on reading ability), Stanovich was able to compare older struggling readers to younger skilled readers. Focusing on the development of phonology or phonologically related access skills, it was demonstrated that good readers possess adequate word identification skills, which facilitate their development of adequate reading comprehension skills. However, Stanovich also cautioned that reading comprehension requires more than adequate word identification skills.

In essence, Stanovich’s work provided support for developmental similarity (continuity) models. He reasoned that poor older readers are developmentally “younger” readers. They follow the same developmental trajectory, but they are progressing at a slower quantitative rate. This distinguishes reading similarity models from the so-called deficit models, which assert that reading differences may also be qualitative, not just quantitative, and that poor readers do not adhere to a similar pathway compared to that of good readers.

With intensive early intervention programs, it may be possible for poor or struggling readers to “catch up”. In general, the evidence for Stanovich’s model is mixed; however, it provides the strongest evidence for problems with decoding (access skills) and even vocabulary development as it affects reading. Recent research on the model suggests that there is some evidence for specific deficits, suggesting qualitative differences, especially for some dyslexic readers [19]. In essence, it is also important to consider sociocultural factors such as the quality of instruction and socioeconomic factors. As discussed later, sociocultural factors present unique challenges for developmental similarity hypotheses. These factors, specifically those associated with neurocognitive research findings, have qualified the similarity construct, leading to the proposal of a developmental similarity (continuity) construct.

Reading models

The similarity (continuity) construct

Most reading models, influenced by the National Reading Panel and the Science of Reading construct, implicitly endorse a developmental similarity (continuity) framework [20,21]. The similarity (continuity) reading models selected as exemplars in this section are the Simple View of Reading [22], Scarborough’s Rope Model (2001), and the Qualitative Similarity Hypothesis [15]. These selected models attempt to explain the acquisition of literacy for both typical and struggling readers by demonstrating that there are similar underlying cognitive processes, such as decoding and comprehension. This acquisition process is qualitatively or developmentally similar (i.e., similar stages, effective strategies), albeit there may be quantitative (i.e., rate or amount) differences due to the efficiency of the use of skills and the influence of sociocultural factors (e.g., language competency, home environment).

Based on extensive research, the National Reading Panel (NRP; 2000) delineated the major components for the development of early reading skills. These components include phonemic awareness, phonics, fluency, vocabulary, and text comprehension. With the work of the NRP as a springboard, the Science of Reading (https://www.thereadingleague.org/wp-content/uploads/2026/05/science-of-reading-defining-guide-ebook.pdf) represents an expansion of reading research, which not only confirmed the original NRP findings but also discussed applications to older and diverse learners, including those with disabilities such as dyslexia, intellectual/cognitive disabilities, autism, and deafness.

The Science of Reading inspired more nuanced models of reading development, exemplified by constructs such as the Simple View of Reading [22], Scarborough’s Rope Model (2001), and Paul’s Qualitative Similarity Hypothesis [15]. These post-NRP models demonstrated that explicit and systematic instruction of the fundamentals (i.e., the NRP components) provides benefits for several struggling readers. In addition, a case was made that the same underlying reading processes (e.g., language and cognitive) apply to most, if not all, learners. This implies that learners follow a similar developmental trajectory in the acquisition of reading skills.

Both the Simple View of Reading [22] and Scarborough’s Rope Model (2001) emphasize two broad processes—decoding and language comprehension. However, Scarborough’s model views reading as an integration of decoding processes involving phonology and sight recognition and language comprehension processes such as vocabulary, syntax, reasoning, and background knowledge. Thus, there are subcomponents within each major component: decoding and language comprehension. As readers develop, these processes become “braided” or integrated. Scarborough’s model is more nuanced than the SVR. Neither the SVR nor Scarborough’s model stipulates separate processes for children with disabilities, nor do they propose alternative pathways. Both models can be used to argue implicitly for the similarity construct.

Related to the SVR and the Reading Rope Model is Paul’s Qualitative Similarity Hypothesis (QSH; [15]. This framework asserts that the development of the English language and literacy skills of d/Deaf and hard-of-hearing (d/Dhh) individuals is qualitatively similar to that of typical (hearing) learners. Despite the fact that the development might be quantitatively slower or delayed, d/Dhh readers proceed through similar stages, employ similar successful strategies, and make similar errors as younger literacy learners. The QSH supports the use of evidence-based practices that are effective for typical learners, but these practices need to be differentiated with respect to the individual profiles of d/Dhh learners. It has been argued that d/Dhh learners can progress and perhaps “catch up” if there are early intervention programs with intensive educational supports [23,24].

The QSH also aligns with the Science of Reading with its emphasis on intensive instruction of the same foundational skills explicated for typical literacy learners. Similar to “hearing” learners, d/Dhh students need to acquire the fundamental structures of English, including phonological processes, and other skills (e.g., vocabulary, comprehension) to learn to read and, specifically, to reach a mature reading competency stage [25]. In essence, the same reading “science” applies to d/Dhh children and adolescents, focusing on English language and reading-related components. There is no strong support for a different, exclusive sign-based methodology [24,26-28]. Although, at present, there have not been any scholarly discussions, it is suggested that the QSH can serve as a basis for implementing Scarborough’s Reading Rope with d/Dhh students

Challenges to the similarity models

Recent studies and meta-analyses strongly support a developmental similarity (continuity) hypothesis; that is, there is a continuity or generalization of extant reading theory that can be applied across populations regardless of ethnicity, gender, sexual orientation, or disability. This is in contrast to previous assumptions of fundamentally different reading mechanisms. However, there are qualifications, especially from neuroscience studies, related to sociocultural variables such as language background, home and cultural values, socioeconomic status, and school literacy practices [17,29,30,]. Although this recent line of research supports a broadly shared underlying developmental system, some scholars still assert that readers may demonstrate qualitatively distinct cognitive profiles or pathways due to sociocultural variables ( [31,32].

The sociocultural variables seem to qualify a strict developmental similarity conclusion. For example, Paul’s QSH asserts that d/Dhh learners, like “hearing” learners, work with similarities with respect to structures (grammar), patterns (letter-sound relations), and reasoning (use of prior knowledge and metacognition). According to the QSH (and other similarity models), these language and cognitive fundamentals do not change across contexts. Nevertheless, sociocultural variables impact how d/Dhh students access, develop, and interpret the fundamentals. In fact, given d/Dhh students’ challenges in developing a first language and other issues such as impoverished home environments and inadequate teacher-student relations, they may have difficulties in acquiring the fundamentals, even with supports. Similar to other struggling readers [30], some d/Dhh students may exhibit different neural patterns—albeit this needs to be confirmed by further investigations.

In essence, sociocultural and other related variables do not alter the fundamentals of learning to read, which are the same for all readers of, for example, English. These fundamentals include [33].

Knowledge of the language of print (i.e., components of english)

Metalinguistic awareness of language- and print-related factors (e.g., of letters, sounds, letter-sound relationships [phonology, orthography], functions of print [pragmatics], words [semantics], sentences [syntax]

Phonological-based working memory or phonological memory (and processes)

Comprehension capabilities (i.e., the development of textual, intertextual, and cultural prior knowledge, metacognitive, and self-regulatory skills)

However, it needs to be acknowledged that sociocultural variables have qualified the similarity hypothesis. Neurocognitive studies have indicated that not all reading differences are purely quantitative. Struggling readers often demonstrate less efficient processing and slower neural connectivity, and this seems to be due to an alteration with respect to, at least, phonological processes [29-37].

This leads to the proffering of a “qualified continuity model,” indicating that the development of reading skills is continuous, but requires specific attention to individual learners’ profiles. These profiles may reveal specific qualitative differences based on the impacts of sociocultural variables. Nevertheless, a nuanced developmental similarity model should attempt to integrate the notions of continuity and constrained differences. To ensure the mature development of reading, researchers and educators need to address the “differences.” The integration of “continuity” and “difference” should provide a better understanding of the reading process, rather than the proffering of exclusive explanations.

This manuscript examined the viability of the developmental similarity (continuity) hypothesis to better understand the reading acquisition process of children and adolescents. Foundational support for the hypothesis was presented via the seminal works of Lenneberg and Stanovich. It was noted that extant reading frameworks averred that common underlying language and cognitive processes apply broadly, with qualifications, across all literacy learners, including individuals with diagnosed disabilities such as intellectual/cognitive, autism, and deafness.

In sum, there is strong support for the developmental similarity models; however, attention needs to be focused on the individual profiles of readers. There may be qualitative differences due to sociocultural and neurocognitive factors such as language background and neural processing abilities. These factors influence the manner in which readers access and develop the foundational reading skills and can impact the subsequent acquisition of mature literacy skills. Nevertheless, the general core requisites remain consistent, indicating that the effectiveness of the models requires an integration of universal shared processes and individual variability. This integration should result in the improvement of reading outcomes, including for students with disabilities.

Recommendations for further research are as follows:

• There is a need for longitudinal and multidisciplinary research, using complex research designs based on extant reading models, to obtain a deeper understanding of the developmental pathways of diverse learners.
• It is critical to conduct neurocognitive investigations to explore the interactions of the physiological processes of the brain with the sociocultural elements of the learning and home environments. This might shed more light on the nature of any qualitative differences and how these differences can be addressed.
• Teacher education programs should provide a curriculum that leads to a broader understanding of the development of literacy skills. This curriculum should include information on extant reading models from multidisciplinary sources.

There continues to be a decline in reading achievement scores, even after the pandemic, for both typical (https://nces.ed.gov/nationsreportcard/reading/) and struggling readers, including those with disabilities (https://www.k12dive.com/news/NAEP-special-education-scores-decline-assessment/739715/). Theorists and scholars should focus on implementation in educational settings, thereby reducing the gap between research and practice. Critical reading skills are becoming even more important for addressing complex problems of technologically infused societies.