The introduction of charter schools into the education system was mainly for improving school outcomes through deregulation with more flexibility and competition. This study presents the empirical evidence of the performances of charter schools on student and school outcomes in the United States by examining a broad array of literature and researches. It is found that the emergence of charter schools has brought about noticeable impact on traditional public schools, although not consistently. Research findings on charter schools and their impact on student achievement are mixed while several studies provide some evidences that charter schools improve student achievement in the early grades. Improvement on methodology is needed to examine the charter school impacts in future studies.