Numerous studies have been conducted to date on the effectiveness of the flipped classroom. However, the results of studies reporting on the model are generally inconsistent. The aim of this research was to evaluate the results of these primary studies in a comprehensive manner, and to obtain general results to document the effectiveness of flipped classroom, also expose the impact of various study characteristics on this effect. To this end, a meta-analysis of primary studies examining the impact of flipped classroom on academic achievement, learning retention and attitude towards course was conducted. 177 studies for the academic achievement, 9 studies for the learning retention and 17 studies for the attitude towards course variables that meet the inclusion criteria were coded and analyzed. Additionally, moderator analyses were conducted for 8 possible moderator variables. The results of the analysis indicated a moderate main effect size for the effectiveness of flipped classroom on academic achievement (g = 0.764) and learning retention (g = 0.601) also a modest main effect size on attitude towards course (g = 0.406). Through to this meta-analysis we have learned that in terms of academic achievement the flipped classroom phenomenon: (1) has been implemented more effectively in small classes; (2) has been applied most effectively in primary schools; (3) its effectiveness has decreased as the duration of implementation extends; (4) has been implemented effectively in almost all domain subjects; and (5) also in terms of attitude towards course and learning retention it has been more effective than traditional lecture-based instruction.