This study examined the relationship between two independent variables, mastery and aptitude, on two dependent variables, achievement and retention. Aptitude was measured by administering the word meaning section of the Iowa Test of Basic Skills. Achievement and retention were measured by a researcher-constructed test. The study involved 17 seventh-grade social studies classes in Dallas, Texas. The students were taught an instructor-developed geography unit with either mastery or nonmastery procedures. The results indicated that the mastery treatment was not superior to the nonmastery treatment in either achievement or retention and that prior verbal ability proved to be the dominant factor in both achievement and retention. References and a listing of procedures followed by mastery and nonmastery groups in the experimental study are included. (Author/DB)