Counselors should have the counseling skills necessary for making adequate therapeutic progress through counseling sessions. Counselors start learning skills and knowledge for counseling in their undergraduate education. During this critical period, the time, form, and quality of the process of gaining core competencies in counseling differ depending on several factors. Supervised sessions might be regarded among these factors. Supervised sessions should be conducted using a comprehensive, objective-driven, and need based model in order for the sessions to be able to reach their goals. Due to the need for more effective supervised sessions, the current study aims to introduce the four-stage supervision model and report preliminary results related to the model's effectiveness. This study consists of 17 counselor trainees studying counseling psychology and the guidance department at a public university during the 2012 fall semester. All participants were enrolled in the Counseling Psychology Practicum. The mixed method design was used in the study. A counselor competencies evaluation form, developed by the researchers, was used in the quantitative phase while semi-structured interview forms were used in the qualitative phase. Pretest and posttest scores of counselor trainees' counselor competencies were provided using the counselor competencies evaluation form. A supervisor and co-supervisor rated the frequency of mistakes that had been made by counselor trainees through counseling sessions to make a frequency chart. The mistakes (ineffectiveness of counseling skills and lack of the required counseling skills) refer to ineffective counseling skills counselor trainees used and counseling skills which they didn't use although they should have been. Wilcoxon signed-rank test and frequency were used in analyzing the quantitative data, and the descriptive method was used in analyzing the qualitative data. Research findings from the quantitative part of the study indicate that counselor trainees made 280 mistakes at 92.71% over the first five supervision sessions, while making 22 mistakes in the last five supervised sessions at 7.28%. These results show that the supervised session conducted based on the four-stage supervision model reduced the counselor trainees' mistakes by 85.43%. Moreover, the results indicate a statistically meaningful difference between counselor trainees' pretest and posttest scores for counselor competencies (z = -3.62; p <.05). According to research findings found in the qualitative part of the study, counselor trainees remarked that the supervised sessions were beneficial for improving their counselor competencies in eight important dimensions. In summary, the four-stage supervision model developed for counselor trainees can be a supervision model that helps counselor trainees enhance their counseling competences. However, the study's findings should be interpreted in terms of its limitations.