In this research, it has been intended to describe pre-service elementary teachers' arithmetical operation skills by handling in learning environments. Case study method was accepted in the research. 80 pre-service elementary teachers studying at a state university in Turkey constituted the study group. The data were obtained through asking four questions to pre-service teachers and collecting answers in writing. When analyzing the data, the error types of pre-service teachers were determined, and the interviews were analyzed through content analysis. It has been pointed out that the pre-service teachers make frequent errors in the arithmetical operation process as a conclusion of the research. These errors intensify in multiplication and division. As a matter of fact, it has been figured out that there were some pre-service teachers who did not make any operations in multiplication and division. In the interviews, the pre-service teachers grounded their errors upon elementary education. They stated that they made continuous errors as they did not have a good elementary education and they did simple errors depending on four operations in the university entrance exam. Once again, two pre-service teachers who did not make any errors grounded this upon good elementary and middle school education.