This study compares the content knowledge of Slovak and Turkish pre-service teachers regarding the classification of the square. The study participants were final year students of training departments for elementary teachers. These pre-service teachers had completed all obligatory geometry courses in their program. For data collection, six questions leading to 10 items for analysis were used in this study. The total correct responses for each item were calculated as percentages for the Slovak and Turkish groups each and a chi-square test of independence was performed to see how well pre-service teachers understood the square in terms of quadrilateral relationships and whether groups of pre-service teachers from different countries displayed significantly different scores. According to the results, the responses of the Turkish and Slovak pre-service teachers were statistically different on each item. Slovak pre-service teachers displayed a significantly higher score on items relating to the class inclusion of a square with a rectangle, a parallelogram, and a quadrilateral. Turkish pre-service teachers presented a significantly higher score for items questioning the class inclusion of a square with a rhombus and a polygon.