Retrieval practice is a learning strategy that has repeatedly been found to have positive effects on memory and learning. However, studies indicate that students rarely use retrieval practice on a voluntary basis. The objective of the present study was to examine students' self-regulated use of retrieval practice, and to determine whether sex and individual differences in cognitive and non-cognitive aspects are related to optional use of practice testing. A classroom study was conducted with 146 upper-secondary school students taking courses in mathematics and Swedish. An ABAB design was used to compare students' optional and non-optional use of retrieval practice (i.e., repeated online quizzing). Students performed cognitive tasks to assess working memory capacity and fluid intelligence and completed self-reports of non-cognitive factors related to school achievement, such as grit, need for cognition (NFC), conscientiousness and openness. Quiz use was then compared using paired- and independent-samples t-tests, and hierarchical linear regression analyses explored relations to individual differences. The results showed that students completed significantly fewer quizzes in the optional sections than in the non-optional sections, and that females completed significantly more optional quizzes than males in Swedish, but not in mathematics. Further, the results showed that conscientiousness predicted optional quiz use in mathematics, whereas sex, NFC, conscientiousness, and openness predicted quiz use in Swedish. To conclude, although the findings show a relatively low optional/self-regulated use of practice testing, in line with earlier research, they suggest that sex and non-cognitive factors, such as personality characteristics, can predict optional use of practice testing.