To participate in today’s society, one has to be able to read and write. For a person with intellectual disability (ID), this requirement may be insurmountable and many never become proficient readers (Cawley & Parmar, 1995; Di Blasi et al., 2019; Lemons et al., 2013; Ratz & Lenhard, 2013a; Wei et al., 2011). Thus, we must provide effective reading instructions early. This study aimed to investigate reading development in individuals with ID enrolled in the Swedish compulsory school system for students with ID using a, for the field, methodologically rigorous design. The study focused on the effects of two reading instruction strategies, phonics-based and comprehension-based, on reading development in beginning readers with ID. The Simple View of Reading (Gough & Tunmer, 1986; Hoover & Gough, 1990; Tunmer & Hoover, 2019) describes reading comprehension as the product of word recognition and language comprehension. The model is supported by meticulous research (e.g., Lervåg et al., 2018; Lervåg & Melby-Lervåg, 2012). Word recognition is the process of correctly identifying meaningful units in text and is associated with several different pre-literacy skills, including phonological awareness. Language comprehension refers to the process of binding together multiple lexical units into coherent semantic representations, using contextual, syntactical, and inferred information. Research has found that individuals with ID have poor pre-literacy skills, word recognition, and reading comprehension. The difficulties for a person with ID also include poor executive functions and working memory, and the difficulties often increase with the severity of the ID. There is a large body of research on reading ability in the population without ID, but the research for persons with ID is lagging (Dessemontet et al, 2019). Recent studies found similar variables associated with word recognition and reading comprehension in individuals with ID as for students with a typical development, suggesting that reading manifests similarly in both groups which in turn would indicate that the methods that are known to support reading development in typically developing children should also produce positive effects on reading development in children with ID. Literature has found that phonic-based interventions are effective for teaching literacy to students with mild ID and students with severe cognitive disabilities (Ainsworth et al., 2016; Dessemontet et al., 2019). Ainsworth et al., (2016) investigated teaching phonics to students with autism, intellectual disabilities, and complex communication needs and found that children increased their letter-sound-knowledge. Dessemontet et al., (2021) performed an RCT phonic-based instruction for students with ID and found positive results. Additionally, studies have shown promising results in combining the instruction of phonic-based and comprehension-based strategies for children with ID (e.g., Browder et al., 2012; Gustafson et al., 2007). However, the samples in the studies are often small without using a control group. The current project builds on these studies using a large-scale controlled study, by implementing a comprehension- and a phonic-based approach (and a combination thereof) using digital media. The aim of the current study is to help children with ID in need of AAC to reach as fluent reading capacity as possible using three different intervention strategies: a phonic-based, a comprehension-based, or a combination of the two.  In the present study, we tested three pre-registered hypotheses (Palmqvist, Samuelsson, et al., 2020):

1. A phonics-based or a comprehension-based reading strategy improves phonological awareness.
2. A phonics-based or a comprehension-based reading strategy improves reading ability (word recognition and reading comprehension).
3. The combination of both reading strategies is more effective than either strategy on its own.

The hypotheses will be tested on these outcome variables: phonological awareness (1, 3), word recognition (2, 3), and reading comprehension (2, 3).

A total of 124 students (ngirls = 54, nboys = 70) were included in the study. They had a mean age of 13.7 years (SD = 3.3) and a mean IQ of 48 (SD = 13). Participants had to attend a Swedish special needs school and be beginning readers. In Sweden, the student receives an ID diagnosis according to the ICD-11 (WHO, 2019) prior to being enrolled in the special needs curriculum. The teachers were instructed to identify students that could not read more than approximately 20 words, which was the operationalization of being a beginning reader. To make the sample representative of the students in special needs schools, no exclusion criteria were set for additional diagnoses or aetiology of the ID. The caregivers of all participating students signed informed consent prior to the testing. The study has been approved by the Swedish Ethical Review Authority (2020-06215). The study is a longitudinal between-group study, with four time points (t1-t4; before, during, directly after the intervention, and a follow-up), and four groups: phonics-based reading strategy, comprehension-based reading strategy, both phonics-based and comprehension-based strategies (combination group), and a comparison group who received teaching-as-usual. Before initiating testing, background information about the participants was collected by interviewing parents (e.g., diagnoses). Testing took place in a silent environment at the participants’ school. All children were assessed on general non-verbal cognitive ability Raven’s 2; Raven et al., 2018), phonological awareness (MiniDUVAN; Wolff, 2013), word recognition (OS64 & OLAF; Magnusson & Naucler, 2010), communication skills (BAF; Frylmark, 2015), and reading comprehension (DLS Bas; Järpsten, 2004), and were allocated into one of four intervention groups. The intervention strategies were provided in a digital format (i.e., apps) and the students worked at school together with a teacher or assistant. The intervention was conducted over 12 weeks (3x30 minutes per week). Linear mixed-effects models were used to evaluate the effects of the intervention. The outcome measures (PA, word recognition, and reading comprehension) were analyzed separately. Days were used as the time variable, starting day 1 at the date of t1. Model fit was assessed using ANOVA. The model with the best fit, indicated by χ2, was chosen. There were three contrasts performed: the comparison group versus the phonics-based intervention (Hypothesis 1), the comparison group versus the comprehension-based intervention (Hypothesis 2), and the combination group versus the phonics-based and the comprehension-based intervention (Hypothesis 3).

No initial differences in reading performance between groups were observed at t1. The results showed that reading improved over time, as indicated by a main effect of time across all three outcome measures β ̂=0.09, 95% CI [0.05,0.13], t(336.07)=4.81, p<.001. The combined phonics and comprehension strategy had a positive impact on phonological awareness development β ̂=0.09, 95% CI [0.03,0.15], t(333.59)=2.78, p=.006. However, no significant differences were found in word recognition or reading comprehension based on the reading instruction strategy used. The results support the idea that systematic instruction that includes explicit teaching of phonics, and comprehension is better than more simple instructional strategies, such as practicing sight-word reading. Phonics-based instruction improves the sensitivity to the sub-lexical structure of spoken words, while comprehension-based instruction leads to richer and more precise lexico-semantic representations. Combining the two strategies may allow students to apply their improved skills in a richer context, making the combination more effective than either strategy alone. The results add to the previous literature that conventional literacy strategies for persons with typical development also are effective for students with ID when using a combined instructional strategy. Teachers should prioritize intensive and methodologically rich literacy instructions for their students. Furthermore, we provide evidence that digitally-based interventions for reading are more effective than teaching-as-usual for students with ID. One reason may be that the digital format enables the instructions to be provided in an adapted manner for students with ID in terms of adapted speed or response time. Additionally, the focused intervention itself might have contributed to more literacy instruction than their teaching-as-usual which in turn resulted in improved reading.

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