University of Iowa

Why the 13 Disability Categories Matter When Planning Reading Interventions

Students and teachers in small-group reading lesson

Understanding the necessity of disability categories is an important step toward using the most effective evidence-based literacy instruction for all students.


Posted on: October 9, 2018

Educators sometimes refer to groups of students using broad strokes, such as English learners or those in special education. Although we should take care not to reduce any child to a single attribute, using classification groups is not simply about assigning labels. Rather, the groups can serve two important functions. First, knowing which students have a certain characteristic can attune a teacher to their learning needs so that proper instruction is planned. Second, identifying members of the defined groups can ensure that the educational outcomes of those students are not lost in the bigger picture of how all students are performing.

For example, the National Assessment of Educational Progress (NAEP) Reading Assessment classifies student performance into achievement levels (basic, proficient, and advanced) based on the score a student earns on a scale from 0-500. The average scale score of all fourth graders who took the 2017 NAEP Reading Assessment was 222 (National Center for Education Statistics, 2017). Although we know this result is below the proficient level, designated as a scale score of 238, the performance of students within classification groups is concealed within these results. That is, students with disabilities had an average score of 187, which was significantly lower than the overall average and indicates that the members of this group were not benefiting as much from the existing reading instruction as their peers. Hence, newly adopted state plans under the Every Student Succeeds Act (ESSA; Every Student Succeeds Act of 2015, 2015) that do not separate the performance of different groups of students has raised concern among education advocacy groups who fear that the most vulnerable students in our schools could fall further behind without triggering the targeted support they need (e.g., Alliance for Excellent Education, 2018).

Federal Disability Categories – A Starting Point for Individualized Instruction

The Individuals with Disabilities Education Act (IDEA; Individuals with Disabilities Education Act, 2004) is the federal law that outlines what states must do in serving children and adolescents ages 3-21 who have been identified as having a disability. Within IDEA, there are 13 disability categories that can qualify an individual for special education services:

Students identified with any of the 13 disabilities may exhibit reading difficulties, but their instructional needs could be quite different. For example, a student who is deaf will need visual cuing systems for learning phonics, but a student with ADD will need a greater emphasis on self-regulation. Even within a given disability category, such as SLD, there are differences in the types of reading difficulties that students experience. They may have a problem with just decoding, or just comprehension, or a combination of decoding and comprehension difficulties. It would be unexpected for students with SLD to struggle with decoding and/or comprehension given that they may exhibit typical performance in other areas (e.g., mathematics) and have intelligence in the normal range. Whereas, students with ID have cognitive limitations that more readily would lead teachers to anticipate literacy difficulties.

Ensuring the Evidence-Based Practice Applies to Your Students

Knowing the particular disability that qualifies a student for special education (as well as the reasons for identifying the student with that disability) makes it more likely that educators can develop an appropriate individualized education program (IEP). This would include identifying effective interventions to improve the student’s reading abilities. Because ESSA still requires that schools adopt curricula and interventions that are evidence based, educators need to know whether the research supporting a given practice was conducted with students who have similar characteristics as those for whom the practice is being planned. Indeed, evidence-based reading practices are not ubiquitous—one strategy would not be considered to work for any and all students. Rather, an evidence base is built in research conducted with particular populations for particular purposes (see our previous blog post that describes what makes a literacy program evidence based).

Recommendations for conducting and reporting high-quality special education research clearly stipulate that study authors provide detailed information on their participants’ disabilities and levels of performance (Horner et al., 2005, p. 167):

…operational participant descriptions of individuals with a disability would require that the specific disability (e.g., autism spectrum disorder, Williams syndrome) and the specific instrument and process used to determine their disability (e.g., the Autism Diagnostic Interview-Revised) be identified. Global descriptions…would be insufficient.

Thorough descriptions of study participants are fundamental to generalizing results to the broader population of students with whom the researchers intended the intervention ultimately would be used (Gersten et al., 2005, p. 154):

Researchers need to provide a definition of the relevant disability(ies) or difficulties and then include assessment results documenting that the individuals included in the study met the requirements of the definition.

This concern with generalizing research results was echoed by the primary professional organization for special educators, the Council for Exceptional Children (CEC, 2014, p. 3):

The study describes disability or risk status of the participants (e.g., specific learning disability, autism spectrum disorder, behavior problem, at risk for reading failure) and method for determining status (e.g., identified by school using state IDEA criteria, teacher nomination, standardized intelligence test, curriculum-based measurement probes, rating scale).

Having researchers transparently identify their study participants is only part of the equation to successfully utilize evidence-based curricula and interventions. Educators and families also need to know—among other detailed information—which of the 13 disability categories applies to a student who needs an IEP. Only then can an IEP team propose appropriate goals, services, measures of progress, and accommodations.


Alliance for Excellent Education. (2018). Too many states minimize student subgroup performance in ESSA accountability systems. Retrieved from

Council for Exceptional Children. (2014). Standards for evidence-based practice in special education. Retrieved from

Every Student Succeeds Act of 2015, Pub. L. No. 114-95, § 114, Stat. 1177 (2015-2016).

Gersten, R., Fuchs, L. S., Compton, D., Coyne, M., Greenwood, C., & Innocenti, M. (2005). Quality indicators for group experimental and quasi-experimental research in special education. Exceptional Children, 71, 149-164. doi:10.1177/001440290507100202

Horner, R. H., Carr, E. G., Halle, J., McGee, G., Odom S., & Wolery, M. (2005). The use of single-subject research to identify evidence-based practice in special education. Exceptional Children, 71, 165-179. doi:10.1111/1467-8578.12095

Individuals with Disabilities Education Act, 20 U.S.C. § 1400 (2004).

National Center for Education Statistics. (2017). National Assessment of Educational Progress (NAEP), various years, 1992–2017 Reading Assessments. Washington, DC: U.S. Department of Education, Institute of Education Sciences, National Center for Education Statistics. Retrieved from