This study aims to reveal how project-based teaching method affects students' achievement, cognitive load and behaviors in programming teaching. In the study, the pretest-posttest, unequaled control group quasi-experimental model, which is one of the experimental models, was used. The participants of the study were sixth grade students who take the elementary school Information Technologies and Software lesson (N = 55). Achievement test, cognitive load scale and behavior management tool ClassDojo were used as data collection tools in the study. In the experimental group, the subjects were taught with project-based teaching method (student-centered and with teacher guidance). Besides, subjects in the control group were taught with traditional teaching method (teacher-centered). The implementation process took six weeks. Two-Factor ANOVA for Mixed Measures was used to examine the difference between the achievement of the groups. At the end of each lesson, the cognitive load scale was applied to the groups and the data obtained was analyzed by using the Cramer V Coefficient. During the study, the students got positive and negative scores according to their behaviors in the classroom, and the significance of the difference between the two percentages was tested according to their positive behavior percentages. As a result of the study, it was found that the academic achievement and in-class behavior scores of students who learned programming with project-based teaching method differed significantly from those who learned with the traditional method. In addition, it was concluded that project-based teaching method used in programming education did not make a significant difference on students' cognitive load.