In this paper we assess the determinants of secondary school outcomes in South Africa. We use Bayesian Averaging Model techniques to account for uncertainty in the set of underlying factors that are chosen among a very large pool of explanatory variables in order to minimize the risk of omitted variable bias. Our analysis indicates that the socioeconomic background of pupils, demographic characteristics such as population groups (Black and White) as well as geographical locations account for a significant variation in pupils’ achievement levels. We also find that the most robust policy determinants of pupils’ test scores are the availability of a library at school, the use of IT in the classroom as well as school climate. This Working Paper relates to the 2013 OECD Economic Survey of South Africa (http://www.oecd.org/eco/surveys/southafrica2013.htm).