The aim of this study is to describe and to explore the main factors affecting the performance of South African pupils in the mathematics test of the Third International Mathematics and Science Study-Repeat (TIMSS-R). The first objective was to describe the performance of the pupils in the mathematics test, the pupils' proficiency in English, as well as describing the background characteristics of pupils, teachers and schools to the extent measured by TIMSS-R. The objective of the second phase was to explore the factors (and their inter-relationships) relating to the pupils' performance and to language proficiency in relation to the background information that was collected from the pupils, teachers and principals of the schools included in the study. Results show that the strength of the language component represented in a number of variables that have strong effects on mathematics achievement is clear. Moreover, the dedication of teachers with regard to their pupils' achievement, as well as the location of the school, are important predictors of South African pupils' achievement in mathematics. (Contains 2 tables.)