This meta-analysis examined if students' writing performance is improved by reading interventions in studies (k = 54 experiments; 5,018 students) where students were taught how to read and studies (k = 36 investigations; 3,060 students) where students' interaction with words or text was increased through reading or observing others read. Studies included in this review involved true- or quasi-experiments (with pretests) written in English that tested the impact of a reading intervention on the writing performance of students in preschool to Grade 12. Studies were not included if the control condition was a writing intervention, treatment students received writing instruction as part of the reading intervention (unless control students received equivalent writing instruction), control students received a reading intervention (unless treatment students received more reading instruction than controls), study attrition exceeded 20%, less than 10 students were included in any experimental condition, and students attended a special school for students with disabilities. As predicted, teaching reading strengthened writing, resulting in statistically significant effects for an overall measure of writing (effect size [ES] = 0.57) and specific measures of writing quality (ES = 0.63), words written (ES = 0.37), or spelling (ES = 0.56). The impact of teaching reading on writing was maintained over time (ES = 0.37). Having students read text or observe others interact with text also enhanced writing performance, producing a statistically significant impact on an overall measure of writing (ES = 0.35) and specific measures of writing quality (ES = 0.44) or spelling (ES = 0.28). These findings provide support that reading interventions can enhance students' writing performance.