This study examined the effects of interleaving and expanding retrieval practice on the retention of physiology concepts. Participants (n = 189) read dozens of immunology and reproductive physiology concepts. Half of the participants read them in a blocked manner (e.g., aabbcc) and the other half in an interleaved manner (e.g., abcbca). Participants were then repeatedly assessed, without feedback, on either a uniform or an expanding series of intervals. Half the participants from both the blocked and interleaved groups completed the assessments 1, 2 and 3 days after reading the passages (uniform), whereas the other half completed them immediately, 1 and 3 days after reading the passages (expanding). All participants completed a post-test 10 days after reading the passages. There were no significant differences in the assessment scores between the interleaved and blocked groups, but the expanding group outscored the uniform group on all four assessments. Mean post-test scores were 47.58±19.81 and 40.11±17.12 for the expanding and uniform groups, respectively (F = 7.25, P < 0.00). In conclusion, participants benefited more from an expanding retrieval practice.