This study was motivated by observations in the field indicating that students at State High School 5 in Jambi City have poor time management skills; for instance, they often arrive late, do their homework in class, frequently neglect or procrastinate on assignments, are unable to set priorities, and prefer engaging in other activities rather than completing their tasks. This study aims to determine the effectiveness of content mastery services using the to-do list technique in improving students’ time management skills. The research design employed is a quantitative study with an experimental approach, utilizing a Pre-Experimental Design with a One-Group Pre-test Post-test Design. The study population consists of 504 students. The experimental class was determined based on interviews with Guidance and Counseling teachers, while the sample was selected using purposive sampling through a simple questionnaire, resulting in a sample of 15 students with low time management skills. Data collection techniques included observation, interviews, and a Likert scale questionnaire. Data analysis was conducted using a paired-sample t-test. The results of the study indicate that the p-value was 0.000 < 0.05, so Ho was rejected and Ha was accepted. This indicates an improvement in students’ time management skills before and after the intervention. Thus, it can be concluded that content mastery services using the to-do list technique are effective in improving students’ time management skills at State High School 5 in Jambi City.