This paper aimed to determine the differences in achievement at the entrance exam between candidates who attended preparatory classes (PC) and those who independently prepared for enrollment at the University of Criminal Investigation and Police Studies (UCIPS). The study included 599 respondents (257 women and 342 men) who were divided into subsamples: 132 women (WPC) and 158 men (MPC) who attended PC and 125 women (WNPC), and 184 men (MNPC) who independently prepared for enrollment in the UCIPS. The entrance exam, in addition to the success from high school, also includes tests for assessment of aptitude and abilities (TAA), namely: the test of knowledge of the Serbian language and literature (TSL), the test of general knowledge (TGN) and test of assessment of general physical fitness (GPF). Differences between groups were determined by t-test for independent samples at a significance level of p <0.05. It was found that WPC had statistically significantly better results from TSL (14.35%) and GPF (14.43%), while no statistically significant difference was found in TGN. In men who attended PC, the results of all TAA segments were significantly better: TSL by 21.17%, TGN by 10.51% and GPF by 27.65%. The obtained results indicate that the structure and manner of performing the PC, which include detailed acquaintance with the procedures, determination of the current level, correction of errors, and recommendations for further improvement, positively impacted the candidates' achievement at the UCIPS entrance exam.