Women remain underrepresented in physical science, engineering, and computer science college majors and careers. Prior research has suggested that motivational beliefs and experiences in high school play a critical role in girls' persistence in science fields. We hypothesized that compared to male students, female high school students may experience less daily autonomy support from teachers and lower psychological need satisfaction in physics, chemistry, and engineering courses. In turn, we expected that these differences would explain girls' lower daily engagement in these courses compared to boys. In line with current trends indicating gender parity in biology and biomedical fields, we did not expect to find gender differences in biology courses. Results from a six-week intensive longitudinal study in which high school students reported their daily experiences of teacher autonomy support, need satisfaction, and engagement during science class supported our hypotheses. The implications of the results for theory and practice are discussed.