It is wellknown that the majority of South African learners achieve extremely poorly in Mathematics. Many claim that one
of the causes of this poor attainment is teachers’ weak knowledge of mathematics, and propose that improving teachers’
mathematical knowledge would improve learner attainment. However, the evidence-base for this proposed solution is
currently relatively weak. We report on a quasi-experimental study examining the learning gains of Grade 10 learners from
five secondary schools in the Johannesburg area, whose teachers participated in a year-long professional development course
aimed at improving the teachers’ knowledge of mathematics for teaching. Statistical analyses of pre- and post-test results
show that the intervention group of learners (N = 586) taught by teachers who had participated in the professional
development (N = 14) outperformed a matched control group of learners (N = 217) taught by teachers in the same schools (N
= 7). An effect size of d = 0.17 for the intervention group is equivalent to two months’ additional progress. While the
learning gains are small, they are statistically significant. These findings provide empirical support for claims that attending
to teachers’ mathematical knowledge can impact learners’ attainment. Suggestions are made regarding the form and
substance of such professional development.

doi: 10.15700/saje.v35n3a1083