Evaluated the achievement effects of an individualized mathematics program designed to solve problems of management, direct instruction, and incentives common to earlier attempts at individualization of instruction. Team Assisted Individualization (TAI), a mathematics program that combines individualized instruction, cooperative learning teams, and direct instruction, was compared to control methods in a 24-wk experiment involving 1,371 students in 59 3rd-, 4th-, and 5th-grade classrooms. Standardized mathematics computations and concepts and application scales served as dependent variables and covariates. Random-effects nested analyses of covariance indicated statistically significant treatment effects favoring TAI for mathematics computations but not concepts and applications. However, individual-level analyses found significant treatment effects for both variables for the full sample and for a subsample of 63 academically handicapped Ss. No Treatment by Handicap interactions were found. (26 ref) (PsycINFO Database Record (c) 2012 APA, all rights reserved)