The purpose with this study is to examine the aspects regarding how laboratory education can affect student’s ability to reason and their motivation for the subject.  To perform this study from a qualitative perspective we have used the method participatory observations. This studies empirical data is based on material from one pre-diagnose, six-lectures and question that mimic interview questions. The concerned subject is mathematics in elementary school grades two and five. This study is based on two theory’s, Self-determination theory that shows prerequisites for internal motivation and Mueller, Yankelwitz and Mahers framework that shows how cooperation affects students ability to develop mathematics argument.  The result shows that students ability to reason primarily are used by an investigating work method in the interaction where students get to discuss to come to a foundational idea and then uses reasoning to solve the assignment. Further the result show that students need of autonomy, competence and inherency needs to be satisfied if the students shall see the mathematic subject as interesting and pleasurable. The conclusions from the study show that if students gets their needs in autonomy, belonging and competence satisfied the knowledge requirements can be easier to reach. This study also shows that the designed working method can stimulate practice of the reasoning ability and strengthen students’ knowledge acquisition.