A number of studies, both small scale and of nationally-representative student samples, have reported substantial associations between school entry math ability and later elementary school achievement. However, questions remain regarding the persistence of the association between early growth in math ability and later math achievement due to the increasing complexity of math knowledge required to be successful in middle and high school. The current study relates both preschool level math skills and growth in math skills over kindergarten and 1st grade to math achievement measured into adolescence. Although it was expected that the association between early math growth and later achievement would decline over time, the study found that early math growth across kindergarten and 1st grade predicts age 15 math achievement as strongly as it predicts 3rd grade achievement. The study results imply the need for high quality math instruction and interventions during the period in which students first begin their primary schooling, as growth during in math ability during early elementary school appears to pay large dividends for achievement into adolescence. Tables and figures are appended.