An independent, quasi-experimental evaluation was conducted involving more than 13,000 elementary-school children in the greater Sacramento, CA area. Nearly 3,800 children received AfterSchool KidzMath for at least one year in 23 Sacramento START after-school settings. This evaluation found that children who received AfterSchool KidzMath for one or more years had, on average, significantly higher math scores on California’s achievement test than those in the control group (after controlling for gender, grade level, ethnicity, language fluency, the percentage of children receiving free or reduced lunch, base API at the school, and parents’ educational attainment). Further, the higher growth rate continued for KidzMath children even after they stopped receiving the program. As might be expected, this differential growth rate diminished over time.