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This blog post is part of our Research Article of the Month series. This month, we summarize “Fidelity of Implementation and Instructional Alignment in Tier 2 Interventions: An Updated Review of Experimental Studies,” a systematic review conducted by researchers at the Iowa Reading Research Center (Young et al., 2026). 

Important words related to research are bolded throughout this post, and definitions of these terms are included at the end of the article in the “Terms to Know” section. Additional terms related to reading instruction can be found in our reading glossary.

Key Takeaways

• Researchers’ reporting of Tier 2 intervention fidelity and details regarding alignment of Tier 1 and Tier 2 instruction has increased over time.
• Information about fidelity of Tier 1 instruction was reported with greater frequency in studies in which both Tier 1 and Tier 2 instruction were researcher-manipulated.

What Did the Researchers Examine?

Multi-Tiered System of Supports in Reading (MTSS-R) is a framework for providing reading instruction and intervention in schools across instructional tiers. Tier 1 refers to core instruction that all students receive, and Tier 2 refers to supplemental intervention provided to some students who require additional support. 

Researchers have evaluated Tier 2 reading interventions in many studies to examine how effective they are at supporting students experiencing reading difficulties. In order to fully understand the effectiveness of a Tier 2 intervention, researchers must also understand the features of Tier 1 instruction and how Tier 2 intervention complements it. 

Thus, the researchers examined the extent to which published studies of Tier 2 interventions reported information about: (a) implementation fidelity of Tier 1 and Tier 2 instruction and (b) instructional alignment of content and approaches across tiers. They reviewed group design studies (e.g., randomized controlled trials, quasi-experimental designs) and single-case design studies. 

Group design studies typically have larger samples, offering a broad perspective on the efficacy of Tier 2 interventions across classrooms and schools in various Tier 1 contexts. On the other hand, single-case design studies generally have fewer participants, allowing researchers to evaluate fidelity and instructional alignment in a more nuanced manner. 

Because of the unique insights each study design affords, the researchers reported the results for group designs and single-case design studies in two separate papers. This month, we summarize the paper focused on group design studies (Young et al., 2026), and next month, we will summarize the paper reporting findings for single-case design studies (King et al., 2026).

What Did the Researchers Find? 

The researchers found that Tier 2 literacy intervention studies commonly reported on Tier 2 fidelity and researcher-manipulated Tier 1 fidelity, but school-implemented Tier 1 fidelity was reported less often. In over 80% of studies, researchers reported information about the features of Tier 1 instruction, but studies varied in the level of detail provided. In studies in which the research team manipulated both Tier 1 and Tier 2 instruction, greater detail was reported about instructional alignment, when reported. Overall, the authors found that reporting on implementation fidelity and instructional alignment has increased since a prior review conducted in 2012 (Hill et al., 2012).

What Are the Implications of These Findings?

Because it is challenging to assess the effectiveness of Tier 2 interventions without understanding how well Tier 1 instruction is implemented and how well it complements Tier 2 instruction, assessing implementation fidelity and instructional alignment serves an important purpose in both research and practice. Rather than evaluating instruction provided in each tier in isolation, the researchers recommend considering how instruction across Tiers 1 and 2 is intentionally coordinated to support students’ learning. 

How Did the Researchers Find This? 

The researchers used a systematic process for searching electronic databases and assessing each search result to determine if it was relevant to the review (Page et al., 2021). They first reviewed study abstracts (brief summaries of the study’s purpose, method, and results), followed by a full-text review to determine if each study met the predetermined criteria to be included in the review. The authors also reviewed the reference lists for all eligible studies that were identified through the electronic database search to identify additional studies that did not appear in the initial search, which yielded two additional eligible articles. In total, the researchers identified 26 group design studies that were eligible to be included in the review. 

Next, they coded each article, which involved recording information such as study characteristics, implementation fidelity factors (e.g., how fidelity was defined and assessed), and instructional alignment factors (e.g., authors’ reporting of the instructional content or grouping). In order to verify that they had accurately identified relevant study characteristics, the researchers calculated inter-rater agreement—a measure of the extent to which two research team members screened or coded studies the same way. Inter-rater agreement was 92–93% for abstract and full-text screening and 95% for coding. 

What Are the Limitations of This Paper? 

It is possible that there are additional studies that may have been eligible to be included in the review but were excluded because information needed to assess eligibility was not explicitly reported. Thus, our understanding of fidelity and alignment reporting in prior research examining efficacy of Tier 2 interventions may be incomplete. 

Terms to Know

• Implementation fidelity: Implementation fidelity refers to the extent to which an intervention is implemented as intended.
• Instructional alignment: Instructional alignment refers to the cohesion of instruction provided across instructional tiers, including shared content and instructional approaches.
• Randomized controlled trial: A randomized controlled trial is a research design that tests how well an intervention works by randomly assigning participants to groups (e.g., a group that receives an intervention compared to a group that does not receive the intervention) and comparing their outcomes after the intervention period.
• Quasi-experimental design: A quasi-experimental design is a research design that tests how well an intervention works by comparing outcomes across groups (e.g., a group that receives an intervention compared to a group that does not receive the intervention) after the intervention period, without randomly assigning participants to groups. 
• Single-case design: A single-case design is a research design that tests how well an intervention works by repeatedly measuring outcomes for a small number of individual participants across different conditions or phases. 
• Systematic review: A systematic review isa review of prior research conducted using systematic procedures to identify relevant literature, assess identified studies for eligibility, and synthesize findings to answer one or more research questions.

References 

Hill, D. R., King, S. A., Lemons, C. J., & Partanen, J. N. (2012). Fidelity of implementation and instructional alignment in response to intervention research. Learning Disabilities Research & Practice, 27(3), 116–124. https://doi.org/10.1111/j.1540-5826.2012.00357.x

Page, M. J., McKenzie, J. E., Bossuyt, P. M., Boutron, I., Hoffmann, T. C., Mulrow, C. D., Shamseer, L., Tetzlaff, J. M., Akl, E. A., Brennan, S. E., Chou, R., Glanville, J., Grimshaw, J. M., Hróbjartsson, A., Lalu, M. M., Li, T., Loder, E. W., Mayo-Wilson, E., McDonald, S., McGuinness, L. A., Stewart, L. A., Thomas, J., Tricco, A. C., Welch, V. A., Whiting, P., & Moher, D. (2021). The PRISMA 2020 statement: An updated guideline for reporting systematic reviews. BMJ, n71. https://doi.org/10.1136/bmj.n71

Young, M. K., King, S., Datchuk, S., McFadden, K., & Yoon, H. (2026). Fidelity of implementation and instructional alignment in Tier 2 interventions: An updated review of experimental studies. Learning Disabilities Research & Practice, 09388982261476719. https://doi.org/10.1177/09388982261476719