The purposes of this study were to investigate the overall effectiveness of extensive reading, whether learners' age impacts learning, and whether the length of time second language learners engage in extensive reading influences test scores. The author conducted a meta-analysis to answer research questions and to identify future research directions. He included two types of empirical studies--those including group contrasts based on a comparison of a control group and experimental groups, and pre-post contrasts that only include experimental groups--in the analysis. After a thorough literature search with numerous search engines and manual and electronic examination of related journals, the meta-analysis included 34 studies (two PhD dissertations and 32 research articles) that provided 43 different effect sizes and a total sample size of 3,942 participants. Findings show a medium effect size (d = 0.46) for group contrasts and a larger one (d = 0.71) for pre-post contrasts for students who received extensive reading instruction compared to those who did not. In sum, the available research to date suggests that extensive reading improves students' reading proficiency and should be a part of language learning curricula.