This study examined the effects of number of illustrative examples and number of practice problems given on seventh graders' achievement in a unit on probability. Four treatment groups were used, one for each combination of two levels of number of examples and two levels of number of practice problems. Prior to treatment students were pretested on the Missing Words test, the Necessary Arithmetical Operations test, computation with rational numbers, and probability. Tests given during and after the programmed treatments concerned computation, relevant and irrelevant attributes of examples, and probability topics. Subscale scores for each test were analyzed using analysis of covariance. Marginally significant results indicated that practice had some effect on relevant and irrelevant concept scales on the first test. The author states that further research on these variables is needed. Computer-generated regression and analysis of covariance tables are appended, as are copies of the tests. (SD)