Computer algebra systems (CAS) are an integrated part of teaching and learning mathematics in upper secondary school, which has resulted in more and more teachers in lower secondary school considering implementing CAS. However, in lower secondary school pupils are introduced to elementary algebra, and CAS-use therefor does not seem as obvious. Indeed, some questions remain, including the following: 1) How is CAS compatible with the current approach to teaching school algebra, when the dominant tasks are solving equations? 2) How can teacher education support preservice teachers in implementing CAS when little well-established knowledge exists about CAS-based teaching? This thesis comprises of a literature review and three papers. The first paper considers the epistemic value of the current paper-and-pencil approach to teaching algebra and how this is influenced by a naïve implementation of CAS. The second paper, on the other hand, studies how CAS can lever the pupils’ knowledge and practice for manipulating and solving equations. The third study examines formats for supporting preservice teachers in developing and formulating knowledge and practice for implementing CAS in the teaching and learning of school algebra.