The aim of this study is to identify -by merging the results of a large number of studies conducted in related literature review-at which level "writing as a process" approach affects students' writing success. Additionally, this paper investigates whether the writing success level differentiates depending on certain study characteristic. Meta-analysis has been preferred as research method in this study and among the studies which are associated with process-based writing practice, only the results of 21 experimental/quasi experimental studies that are conducted in Turkey have been synthesized which meet the inclusion criteria. In this regard, effect size measures (Hedge g) of studies included into meta-analysis, heterogeneity, publication bias tests and intervening variable analysis have been done with the use of Comprehensive Meta Analysis v2.0 (CMA) software. In the results of study, Hedge g=0,983 has been determined as the corrected effect size related to effect of process-based writing approach on students' writing success levels. This value indicates that process-based writing approaches affect students' writing success levels to a large extent. The results of this study reveal that -in spite of teaching levels-process based writing model, duration of practice, text type used in practice and publication type in which practice has been reported do not make a statistically significant difference in effect sizes.