One of the components of the response-to-intervention model is the provision of an effective first level of intervention to all students in the classroom. The purpose of this article is to define the elements that make up this first level of intervention in mathematics. To do this, we discuss what needs to be learned by the students and propose a particular pedagogical approach. The learning goals are broken down into three skill dimensions that must be developed for all mathematical concepts : conceptual understanding, fluidity and flexibility. We also discuss the importance of using different ways of representing a concept. To achieve this learning, problem solving is shown as an effective pedagogical practice. Finally, we describe the main steps in the process of teaching mathematics with problem solving and we discuss some associated issues.