The purpose of this report is to examine the extent to which participation in the Los Angeles Better Educated Students for Tomorrow (LA's BEST) afterschool program leads to positive achievement outcomes in math and English-language arts. A quasi-experimental design is utilized, and hierarchical linear modeling (HLM) is employed to examine the relations between intensity of program participation and achievement outcomes across 4 years of data using two cohorts of students. Results reveal that regular attendance (over 100 days per year) in the LA's BEST afterschool program leads to higher achievement in California Standards Test (CST) math performance but not in CST English-language arts performance. Therefore, LA's BEST can improve their program outcomes by setting program structures, activities, and policies to encourage all students to attend regularly. (Contains 9 tables and 2 footnotes.) [This report was supported by grant number 021891 from LA's BEST. ]