Background:
Preservice teachers need to know how to make and use manipulatives that stimulates students’ thinking as it is a crucial competency..

Material and methods:
We focused on changes in the ideas and knowledge of 20 preservice teachers engaged in action research with a teacher educator. Over the course of 14 weeks, this study examined preservice teachers’ design ideas and their use of manipulatives in teaching mathematics. Data were gathered by using interviews and questionnaires to explore how the preservice teachers devise new manipulatives.

Results:
Two categories and sub-categories were subsequently assigned as a result of the analysis. These categories are related to the processes that the participants experienced. During the first phase the participants focused on suggesting an idea and in the second phase they attempted to put this idea into practice.

Conclusions:
It was concluded that the preservice mathematics teachers are struggling to develop new ideas for an appropriate manipulative material design. They encountered structural difficulties when they attempted to transform their ideas into concrete models. Moreover, their ideas and designs sometimes can be very different from manipulatives designed by experts.