Increasing teacher quality is a major objective of recent Cambodian education policy. In mathematics education literature, pedagogical content knowledge (PCK) has emerged as a critical component of teacher quality that is strongly linked to student achievement. In this study I use data from a large survey of Cambodian schools to investigate the effect of math teachers' PCK on third grade student achievement. I use ordinary least squares and Quantile Regression analyses to examine this aspect of teacher quality. I find that pedagogical knowledge is a strong predictor of student math achievement in Cambodia in comparison to other student, school, and background variables, but that the effect is concentrated among higher achieving students. Quantile Regression with this dataset also exposes gaps and thresholds in achievement associated with other explanatory variables. In addition, I investigate the proportional distribution of teacher PCK in Cambodia and find that lower quality teachers are more likely to be teaching lower achieving students of lower socioeconomic status.