The Problem Solving Approach is preferred for developing children who learn mathematics by /for themselves. The task for the Problem Solving Approach is indicated by a slider mark in the textbook. Normally, the tasks are sited on the odd number pages. At the slider mark, the problematic is written by means of questions from children or the key mark. The children's various ideas are explained on the even number pages, because the children cannot see the even number pages when reading about the task on the odd number page. Through the explanation and comparison of the various ideas, the children are able to learn and the teachers can continue from the various ideas. If you open the textbook, you may recognize a lot of slider marks which have this style. Figure 9 is a good example. All those marks are the result of lesson studies.