AbstractBackgroundObjectives: This pre-registered systematic review and meta-analysis aimed to answer if K-2 students at risk (Population) for reading impairment benefited from a response to tier 2 reading intervention (Intervention) compared to teaching as usual, (Comparator) on word decoding outcomes (Outcome), based on randomized controlled trials (Study type).MethodsEligibility criteria were adequately sized (n> 30 per group) randomized controlled trials of tier 2 reading interventions within response to intervention targeting K-2 at risk students (percentile 40) compared with teaching as usual (TAU). Reading interventions had to be at least 20 sessions and conducted in a school setting with at least 30 students in each group and containing reading activities. TAU could not be another intervention. Only decoding tests from WRMT and TOWRE were included. Information sources: Database search was conducted 190520 in ERIC, PsycINFO, LLBA, WOS and additionally in Google Scholar as well as a hand search in previous reviews and meta-analyses. The searches were updated in 2021-03-21. Risk of bias: Studies were assessed with Cochrane’s Risk of Bias 2, R-index and funnel plots. Synthesis of results: A random-effects model was used to analyze the effect sizes (Hedges’ g)ResultsIncluded studies: Seven studies met the eligibility criteria but only four had sufficient data to extract for the meta-analysis.Synthesis of results: The weighted mean effect size across the four included studies was Hedges' g = 0.31 95% CI [0.12, 0.50] which means that the intervention group improved their decoding ability more than students receiving TAU. A Leave-one-out analysis showed that the weighted effect did not depend on a single study. Students at risk of reading difficulties benefit from tier 2 reading intervention conducted within response to intervention regarding a small effect on the students decoding ability. DiscussionLimitations of evidence: Only four studies met inclusion criteria and all studies had at least some risk of bias.Interpretation: Tier 2 reading interventions, conducted in small groups within RtI, can to some extent support decoding development as a part of reading factors. Other:Funding: Thomas Nordström and Rickard Carlsson was supported by the Swedish Research Council (grant no. 2020-03430). Camilla Nilvius was supported by Swedish National Research School Special Education for Teacher Educators (SET), funded by the Swedish Research Council (grant no. 2017-06039).Registration: Available at the Open Science Framework: https://osf.io/6y4wr