This research was carried out to investigate the effect of graphing calculator program supported problem solving instruction on mathematical achievement and attitude in transformation geometry subject. The study was carried out with 49 seventh grade students in a middle school in Balikesir province. A pre-test post-test quasi-experimental design with two groups was used in the study. The experimental group received transformation geometry instruction supported by a graphing calculator program, while the control group received transformation geometry instruction without using any technological material for 6 weeks. Achievement of the students was assessed with the Transformation Geometry Achievement Test, while their attitudes were assessed with the Geometry Attitude Scale. For the analysis of the data obtained from the tests, independent samples t test and Two-Way ANOVA for Mixed Measures were used. As a result of the analysis of the data, a positive significant difference was obtained in favor of the experimental group for the mathematical achievement, while there was no significant difference between the experimental and control groups for attitudes towards geometry. Controlling the gender variable, the ANCOVA test was applied to attitude scores and a positive significant difference was obtained in favor of the experimental group. Reflective observation forms and interviews were used to collect qualitative data. Qualitative data were analyzed by descriptive content analysis and divided into themes and codes. As a result of the analysis, it was determined that the students in the experimental group generally stated that the graphing calculator program made their knowledge permanent, facilitated their learning, developed a positive attitude towards the lesson and made the lesson enjoyable.