This meta-analytic synthesis of evaluation findings from 40 studies showed that students can raise their scores on aptitude and achievement tests by taking practice forms of the tests. The size of the gains from practice appeared to be a function of three factors. First, gains were larger when identical forms of a test were used for practice and criterion measurement and were smaller when parallel forms were used. Second, the size of the effect increased with the number of practice tests given. And finally, the size of effect was influenced by the ability level of the population studied; gains were larger for subjects of high ability than they were for subjects of low ability.