Digital technologies shape the processes of teaching and learning in the classroom. They create spaces for action, while at the same time they pose restrictions and can generate unexpected situations, both for teachers and students. In this paper, we show examples in which teachers respond to contingencies emerging from the use of interactive programs in the classrooms. By describing different ways in which teachers react to those contingencies, we show how the technology plays an important role, at times by creating unexpected situations, and at others in support of teachers' explanations. In both cases it can promote modifications in students' actions and shape teachers' actions and responses in relation to a particular mathematical situation or problem. Understanding how teachers react when they are faced with an unexpected situation is important in order to gain knowledge about those particular responses that result in effective behaviors that are related to mathematics learning, and also in terms of the construction of rich learning environments that promote those kinds of behaviors. Results show that the kind of interaction that technology has the potential for promoting plays an important role in making students and teachers more aware of students' doubts and misunderstandings, but that this potential needs to be accompanied by effective teachers' strategies through which they use contingencies as opportunities to promote both their own and their students' learning. This study contributes to deepening knowledge about teachers' effective strategies in primary school classrooms as well as providing examples to promote reflection regarding teachers' training programs.