Examined were the effects of varying the number of practice problems in a programed unit on negative bases designed for high school students. A sample of 421 students from grades 9 through 12 was divided into three groups on the basis of amount of mathematics coursework completed. Students were given four pretests (numeration, arithmetic reasoning, bases, and problems) followed by a pre-program designed to familiarize them with programed text materials. They were then assigned to treatment groups for instruction; materials were identical for the two groups except version F had only 1 or 2 examples for each explanation while version M had 4 or more. The posttest consisted of the Negative Number Base Achievement Test and Word Association Test. Means, standard deviations, and reliabilities were computed for all tests and subscales and data were submitted to regression analysis. Results indicated that increasing the number of practice problems improved student learning; there was an interaction between students' mathematical sophistication and the levels (e.g., comprehension) at which the improvement took place. (SD)