  Students' high school decisions will always impact efforts to achieve gender
parity in STEM at the university level and beyond. Without a comprehensive
understanding of gendered disparities in high school course selection, it will
be impossible to close completely the gender gap in many STEM disciplines. This
study examines eleven years of detailed administrative data to determine
gendered enrolment trends in university-stream secondary school STEM courses.
Male and female enrolments for all publicly funded secondary schools across the
province of Ontario (N = 844) were tracked from the 2007/08 academic year to
2017/18. The data reveal a clear trend of growing enrolment in STEM
disciplines, with the increase in female students continuing their STEM
education significantly outpacing males in almost all courses. However, these
results also demonstrate the disparities that persist across STEM disciplines.
The existing gender gap in physics remains large - in 2018, the median grade 12
physics class was only $36.5\pm0.05%$ female - with virtually no progress
having been made to close this gap. By tracking individual student cohorts, we
also demonstrate a newly discovered result showing the continuation rate of
male students in biology stream courses has experienced a precipitous drop-off.
The proportion of male students continuing from grade 10 science to grade 12
biology two years later has seen an average yearly decline of $-0.44\pm0.08$
percentage points, potentially foreshadowing the emergence of another
significant gender gap in STEM. We suggest that researchers and educators cease
treating STEM as a monolith when addressing gender disparities, as doing so
obscures significant differences between disciplines. Future efforts,
particularly those aimed to support women in STEM, must instead adopt a more
targeted approach to ensure that they solve existing problems without creating
new ones.
