The objective was to examine the impact of different types of accommodations on performance in content tests such as mathematics. The meta-analysis included 14 U.S. studies that randomly assigned school-aged English language learners (ELLs) to test accommodation versus control conditions or used repeated measures in counter-balanced order. Individual effect sizes (Glass's d) were calculated for 50 groups of ELLs and 32 groups of non-ELLs. Individual effect sizes for English language and native language accommodations were classified into groups according to type of accommodation and timing conditions. Means and standard errors were calculated for each category. The findings suggest that accommodations that require extra printed materials need generous time limits for both the accommodated and unaccommodated groups to ensure that they are effective, equivalent in scale to the original test, and therefore more valid owing to reduced construct-irrelevant variance. Computer-administered glossaries were effective even when time limits were restricted. Although the Plain English accommodation had very small average effect sizes, inspection of individual effect sizes suggests that it may be much more effective for ELLs at intermediate levels of English language proficiency. For Spanish-speaking students with low proficiency in English, the Spanish test version had the highest individual effect size (+1.45).