In the Iranian educational system, Mathematics has a high position in the school curriculum. However, there are barriers to teaching and learning Mathematics, the recognition and resolve of whom has been and is one of the main concerns of math educators. The concept under study in this research is the concept of Limit, since the students have difficulty in understanding it. The aim of the present study is to analyze and study the students' understanding of the concept of Limit by emphasizing the control of Schoenfeld according to the APOS theory. The study sample is 50 male students of the eleventh grade of Mathematics and Physics in Bandar Anzali city in the academic year of 2018-19, who were randomly selected by cluster sampling method. The test tool is a questionnaire consisting of 6 questions designed by the researcher. The reliability of the test is attested by Cronbach's alpha calculation of 0.793 for the pretest and 0.812 for the posttest. The results of the study showed that the control factor is effective in increasing students' understanding of the subject of Limit based on APOS theory. On this basis, the greatest effect of the Schoenfeld control factor is on the schema and object levels, respectively. The Schoenfeld control factor had little effect on the next two levels, meaning practice and process. However, the change in the process level is slightly greater than the practice level.
