This systematic review summarizes effects of peer tutoring delivered by non-professional tutors, such as classmates, older children and adult community volunteers, to children between 5 and 11 years old. Inclusion criteria for the review included tutoring studies with a randomized controlled trial design, reliable measures of academic outcomes and a duration of at least 12 weeks.. Searches of electronic databases, previous reviews, and contacts with researchers yielded 11,564 titles. After screening, 15 studies were included in the analysis. Cross-age tutoring showed small significant effects for tutees on the composite measure of reading (g=0.18, 95% CI: 0.08, 0.27, N=8,251), decoding skills (g=0.29, 95% CI: 0.13, 0.44, N=7,081), and reading comprehension (g=0.11, 95% CI: 0.01, 0.21, N=6,945). No significant effects were detected for other reading sub-skills or for mathematics. The benefits to tutees of non-professional cross-age peer tutoring can be given a positive, but weak recommendation. Effect Sizes were modest and in the range-0.02 to 0.29. Questions regarding heterogeneity of effects, study limitations, lack of cost information and the relatively few number of studies that have used a randomized controlled trial design means that the evidence base is not as strong as it could be. Subgroup analyses of included studies indicated that highly-structured reading programs were of more benefit than those that were loosely-structured. Large-scale replication trials using factorial design, process evaluations, reliable outcome measures and logic models are needed to better understand under what conditions, and for whom, cross-age non-professional peer tutoring may be most effective.