The study addresses the question of what makes a mathematical task interesting to the 9th year students. Semi-structured interviews were carried out with 15 students of purposive selection of the 9th year. The students were asked to recall a task they found interesting and engaging during the past three years. An analysis of the tasks was made with respect to the context, cognitive demand, and task structure, while interview data were analyzed using the Theory of Didactical Situation (TDS) and Mathematical Task Framework (MTF). The students recalled a total of four teacher-designed tasks. All of the tasks offered a high level of challenge, elements of sharing and some freedom of choices related to the aspects of the tasks. The results showed that in most cases the students pointed out the target knowledge as the reason for a task to be interesting and engaging, followed by the way the content was dealt with in the classroom.