Teaching is a very complex process that involves individual beings with individual abilities and needs. Since “psychology has found out that people are different”, modern didactic demands a type of instruction that responds to the individual learning conditions of each student. The target of an individualized instruction is to give all students the chance to realize their potential and to support all students to perform best within their abilities. Individualization concerns teaching in all grades, school types and subjects. Student achievement in primary school forms the basis of the following educational career. In regard to this it seems necessary that instruction in primary school is able to provide children with equal opportunities. Primary schools should offer optimal instruction that adjusts to the children’s developmental levels, their individual needs and interests. Nevertheless, traditional teaching in Austria characteristically involves homogeneous and selective methods rather than addressing individual needs or implementing methods that support inclusion. This is also supported by results of a national study conducted within PISA 2003, that deals with mathematics instruction in secondary school (Schwantner & Schreiner, 2006). The present research focuses on primary school mathematics teaching, self-beliefs and student achievement in mathematics.