This research project undertook a review and synthesis of previous research on the effectiveness of feedback for individual writing development. The work plan was divided into two main phases. First, we surveyed all available studies that have investigated the effectiveness of writing feedback, including both quantitative and qualitative research, for students who have learned English as a first language (L1-English), students who have learned English as a second language (L2-English), and students who have learned second languages other than English. The results of this survey are described in a narrative overview of previous research pertaining to the role of feedback in the development of writing proficiency. The survey also identified the major theoretical constructs used in this research domain, providing the basis for subsequent statistical analysis. Second, we built on this survey to carry out a meta-analysis of empirical studies in this research area. The goal of the meta-analysis was to provide a quantitative investigation of the extent and ways in which feedback has been effective, summarizing the findings of previous quantitative studies that have employed suitable statistical measures. Several analytical steps were required for the meta-analysis: developing a coding rubric; analyzing the research design and adequacy of reporting in studies to determine if they were suitable for inclusion; coding each study for all relevant research design factors; computing effect sizes for each study; and analyzing and interpreting the general patterns that hold across this set of studies. The meta-analysis compared the gains in writing development with respect to several different kinds of feedback. Overall, feedback was found to result in gains in writing development. Beyond that, there were several predictable findings (e.g., that written feedback is more effective than oral feedback for writing development) and several other more noteworthy trends (e.g., that peer feedback is more effective than teacher feedback for L2-English students; commenting is more effective than error location; and in general, focus on form and content seems to be more effective than an exclusive focus on form). [A list of studies used for the research synthesis is included.]