Objective: Team cohesion is considered a critical factor in achieving success in team sports, as it enhances coordination and cooperation among team members. Therefore, the present study aimed to compare the level of cohesion between successful and unsuccessful girls’ volleyball teams in national high school competitions during the year 2022. Methods: The statistical population consisted of 105 team members, with a mean age of 16.24 ± 0.82 years. Data were collected using the standardized Group Environment Questionnaire (GEQ), which measures four dimensions of cohesion: individual task cohesion, individual social cohesion, group task cohesion, and group social cohesion. Descriptive statistics along with the Kolmogorov-Smirnov test, independent t-test, and Mann-Whitney test, were used for data analysis in SPSS version 22. Results: Findings indicated that successful teams had significantly higher mean scores in all dimensions of group cohesion—including individual task cohesion, individual social cohesion, group task cohesion, and group social cohesion—compared to unsuccessful teams (p < 0.05). Conclusion: Based on these findings, it is recommended that fostering and strengthening team cohesion be considered an effective strategy to enhance the performance of sports teams, particularly at the school level.