This study has investigated the take-up, at a range of South African tertiary institutions, of Open Educational Resources (OER) designed for mathematics teacher education. Although numerous studies (e.g. Darling-Hammond, 2006; Jonassen & Rohrer-Murphy, 1999; Loughran, 2006) have identified criteria for the development of quality materials for teacher education, and have investigated ways in which these have been and should be used, little attention has been paid to the implications of these findings for the use of OER in teacher education. In 2006 the South African Institute of Distance Education (SAIDE) initiated the ACEMaths project to pilot a collaborative materials design and adaptation process in response to a Department of Education call for large scale teacher upgrading programmes leading to an Advanced Certificate in Education (ACE) in priority areas. Nine South African tertiary institutions formed the collaborative group for the development of Mathematics teacher education materials. Six of these institutions committed to using the pilot materials in their teacher education programmes in 2007. Methodologically, the research is a case study of cases (Adler & Reed, 2002), in which the varying uses of the materials in these six institutional sites constituted the individual cases. At each site data were gathered from session observations, questionnaires and interviews. Artefacts, such as examples of customised materials, were also collected. Cross case analysis revealed that institutions used the ACEMaths materials in both similar and different ways and in a range of programmes. Findings from this analysis and their implications for both initial inter-institutional designing and subsequent intra-institutional re-designing and re-use of OER are discussed.