There are a number of papers on Mathematics teaching where contextualized problems are intended to be developed as starting point for the different subjects of the lesson, even if they lack support on a theory which tells how to do it properly. Dutch researchers such as Hans Freudenthal have developed the Realistic Mathematics Educational Theory (RME) where contextualized problems are the fundamental principle along with some other kind of problems that help the implementation of this in the class room. This theory has been applied at several schools and in textbooks in Holland showing excellent results on the students’ side, especially when it comes to international level test. This paper makes use of this theory as framework for designing the activities and it is based on Wenger’s communities of practice applied to students.