This study aimed to determine the effect of the activity-based environmental education course on the attitudes and behavior levels of the students of the child development program concerning environmental problems. The study was prepared by using the explanatory sequential design, one of the mixed method patterns in which qualitative and quantitative data are used together. While one-group pretest-posttest experimental design was used in the quantitative dimension of the study, phenomenology was employed in its qualitative dimension. The sample group of the study was composed of 60 first-year students attending Kayseri University Hüseyin Sahin Vocational High School Child Development Program in the 2019-2020 academic year (spring semester). Within the scope of the environmental education course, activity-based practices were performed with the students for 6 weeks. The students were divided into groups and one group applied the related activities they prepared with their friends in the classroom each week. Before and after the application, 'The Environmental Problems Attitude Scale' developed by Güven (2013) and 'The Environmental Problems Behavior Scale' developed by Güven and Aydogdu (2012) were applied for the students. After collecting the quantitative data, 10 students were interviewed via a semi-structured interview form and their opinions on the activities were collected. Kolmogorov-Smirnov test for normality, t-test and Wilcoxon signed-rank test were used to analyze the qualitative data of the study. The qualitative data of the study were analyzed based on descriptive analysis. As a result of the study, it was determined that after the activity-based practices performed in the environmental education course, the scores of the attitude and behavior of the students concerning environmental problems increased. As a result of the interviews made with the students, it was found that the students had both positive and negative opinions on the activities conducted in the course. By these activities, the students emphasized that they had cognitive and affective acquisitions in the environmental education course. Finally, the students stated that they acquired awareness, consciousness, and responsibility about the environmental problems along with these activities.