Can providing learner support materials, particularly custom-designed workbooks, improve primary mathematics achievement more cost effectively than providing conventional textbooks? To contribute to this debate, this paper reports on the findings of a study conducted in 2010 by a consortium of educational researchers at JET Education Services and University of the Witwatersrand. Between January and June 2010, the consortium undertook a randomised control trial of learning support materials in Grade 6 classes in 44 primary schools serving low income communities in Gauteng province. The study shows that Grade 6 learners exhibit the same degree of learning improvement in mathematics, whether they use a conventional textbook or a workbook specifically customised to address the problems exhibited by South African learners. From a policy perspective, no warrant can be issued on the relative effectiveness of the specific workbooks considered in the study.