This paper is focused on understanding if the use of interactive activities based on problem solving and automatic formative assessment in a blended learning environment can promote the development of engagement in Mathematics for students of grade 8. In this context, engagement is characterized as a multidimensional construct composed of an emotional component, a cognitive component and a behavioral one. The discussion is based on the results of a didactic experimentation conducted with 299 students of grade 8 who, during one entire school year, had access to an online platform rich in interactive learning materials used in blended modality. Through an initial and a final questionnaire, evolutions in their engagement levels were measured. We found that the initially most disengaged students and those coming from lowest social classes are those who mainly benefitted of the interactive activities in order to improve their engagement levels.