This is supported by Cohen et al who state that “children's characteristics go beyond simply their preferences for learning and include, for example, their interests, concept of oneself, motivation, degree of autonomy” (2004, p. 137). Furthermore, O'Brien and Guiney (2001, p. 11) argue that the diagnosis of student performance arises from very complex interactions and define differentiation (p. 10) as a concept that must be viewed inclusively and applied to all . With this in mind, a mathematics teacher, who was observed teaching the highest and lowest groups (better English and weaker English), designed her lessons. Despite the fact that each group was relatively homogeneous in terms of language ability, both were mixed ability groups in the characteristics described by Cohen et al (2004, p. 136). In both classes, the teacher was observed using a variety of differentiation strategies such as pair work, group work, and peer assessment. After setting the tasks, it was also observed that the teacher gave more individualized attention to the weaker students and more independence to the stronger ones. Additionally, when a student needed help at a time when the teacher was busy helping another student, the teacher often assigned a stronger student to help his or her peer. Having a stronger to help