The aim of this study is to investigate student engagement from the point of view of the teacher, by focusing on teacher's didactical strategies used to engage students during algebra introduction. Eight teachers in grade 6 and 7 participated in a focus-group interview study. The findings are based on episodes of student engagement in algebra and teachers' discussions of didactical strategies used to enhance student engagement, analysed using the Theory of Didactical Situations. The results show that teachers put organisation of the lesson and issues related to the didactical contract in the foreground, while content and mathematical problems seemed taken for granted, as given by the textbook or curriculum. Teachers' freedom to influence the didactical design was thereby constrained to shaping activities and norms regulating interaction in the classroom. Among these norms they specifically emphasized the value of student reasoning.