Scheme holds an important role in problem solving process. Scheme will determine an action that must be done in  problem solving. Problem solving is one of abilities that must be owned by every person. This ability is important because in our life we often face a problem that of course  the solution must be found. Problem solving involves two aspects namely problem that needs to be solved and knowledge (scheme) owned. The two aspects will keep interacting until the  solutions of the problem could be found. Interaction can happen through the processes of assimilation and accommodation. Assimilation and accommodation are the processes done by  someone for combining new information acquired or problems encountered into the schemes that have been owned.

This study aimed at describing the use of scheme that had been owned in problem solving through the processes of assimilation and accommodation. The research subject was the student who had studied flat geometry. Data were collected through initial scheme test, problem-solving test, and interview. The subject did an initial scheme test. It is to ensure that the subject had a scheme related to the problem solving test given later. The interview was conducted to ensure that the answers of the problem solving test written down by the subject was an overview of the use of the scheme already owned in problem solving through assimilation and accommodation processes.

Based on the results and data analysis, it is concluded that there are 3 cases of scheme use in problem solving through assimilation and accommodation. They are: 1) using the scheme which is not suitable and cannot change it. In this case, the problem solving done by the subject is dominated by the assimilation process. Subject was unaware of the inappropriate scheme that was used in problem solving, 2) using inappropriate scheme and can change it. In this case, the subject did assimilation in problem solving. However, the subject was aware of the inappropriate scheme that was used in problem solving, so that the subject did accommodation and could use the appropriate scheme in problem solving, and 3) using the appropriate scheme. In this case, the problem solving done by the subject is dominated by the assimilation process. The subject could use the appropriate scheme in problem solving.

Having a scheme that suits the problem faced is not enough to determine the success of problem solving. It requires conformity in using the scheme owned through assimilation and accommodation to help the success in problem solving. In problem solving, there are three cases of scheme use: 1) using an inappropriate scheme and cannot change it, 2) using an inappropriate scheme and can change it, and 3) using the appropriate scheme. As a process, it allows assimilation and accommodation to be imperfect. Assimilation and accommodation processes should be able to be controlled to avoid the inappropriate use of scheme in problem solving.