This REL West study explores the prevalence of students repeating Algebra I, who is most likely to repeat the course, and the level of improvement for students who repeat. Using six years of data from a cohort of 3,400 first-time seventh grade students in a California school district, authors found that 44 percent of students repeated algebra I. Overall, student performance improved on average by approximately one-half of a letter grade and a little less than one-third of a performance level on the CST when students repeated the course. But when the data was disaggregated based on initial performance in the class, higher-achieving students experienced variation in improvement levels. Repeating students who initially received average course grades of at least a "C" in Algebra I earned higher CST scores but lower course grades on average when they repeated the course. Students who initially scored Proficient on the Algebra I CST experienced increases in course grades but declines in CST scores on average when they repeated the course. Overall, these findings show that lower-performing students are likely to experience improvements in grades and CST scores when they repeat Algebra I, but that higher-performing students are likely to experience improvements on some measures of performance and declines on others when they repeat the course. The following are appended: (1) Detailed information about the dataset and analysis; and (2) The multivariate analysis, multiple repeaters, and summer repeaters.