Özet:

The aim of this study is to examine the development of pre-service mathematics teachers' proof-writing skills in teaching activities based on the van Hiele model. The study was carried out with 10 pre-service mathematics teachers studying in the first year of the primary school mathematics teaching programme. In the study, teaching experiment design, one of the qualitative research methods, was adopted since it was aimed to reveal the effectiveness of the van Hiele model on pre-service mathematics teachers' proof-writing skills. For this purpose, qualitative data collection tools (personal interviews, pre-service teachers' worksheets, and researcher field notes) were used to collect data. The development of pre-service mathematics teachers' proof-writing skills was discussed within the scope of teaching stages and levels in the van Hiele model. As a result of the study, it was seen that the pre-service mathematics teachers' proof-writing skills were supported by a developmental process in the van Hiele model, and they were able to reach the van Hiele-4 level in proof-writing. It was concluded that knowledge and inquiry, guidance/directed orientation, explicitation/interpretation, free guidance and integration, which are the components of the teaching environment in the van Hiele model, are effective in supporting the pre-service mathematics teachers developmentally. In line with these results, suggestions were made to support the development of van Hiele geometric thinking in geometry learning of pre-service mathematics teachers.