In this study of 431 Grade 9 and 10 students, we investigated gender and frequency of practical work as determinants of science students' perceptions of their learning environment and attitudes. We assessed classroom environment with the Science Laboratory Environment Inventory (SLEI) and attitudes with the Students' Adaptive Learning Engagement in Science (SALES) questionnaire and a scale involving students' future intentions to study science. The surveys exhibited sound factorial validity and reliability. Interesting differences were found in the learning environment and student attitudes according to student gender and three different frequencies of practical work (namely, at least once a week, once every 2 weeks, or once every 3 weeks or more). More-frequent practical work was more effective than less-frequent practical work in terms of perceived open-endedness, integration and material environment in the laboratory environment and more-positive task value and self-regulation attitudes (with modest effect sizes exceeding one-third of a standard deviation). Although small gender differences existed for some scales, increasing the frequency of practical work was not differentially effective for male and female students.