The aim of this study was to investigate primary school students’ proof schemes for four operation problems in mathematics. Based on qualitative research design, the data were collected through document analysis and interview method in the study. In the first stage of the study, 4 open-ended four operational problems were asked to al of 1st, 2nd and 3rd Grade students in a primary school located in the city center of Elazig. Students who answered the problems correctly were invited for interviews. In the interviews, the students were asked to explain aloud how they solved the problems. The interview data were analyzed using descriptive analysis based proof schemes categorization of Harel and Sowder (1998), and the proof schemes and proof-making approaches of the participants were investigated. The findings revealed that the participants mostly used external conviction proof schemes regardless of grade and operation type. It was also found that although 1st Grade students used the authoritarian proof scheme more, 2nd and 3rd Grade students mostly employed ritual proof scheme to explain their solutions.