To understand the implementation quality of the Tier 1 Program (Secondary 1 Curriculum) of the Project P.A.T.H.S. (Positive Adolescent Training through Holistic Social Programmes), observers carried out process evaluation in the form of systematic observations of 22 units in 14 randomly selected schools. Results showed that the overall level of program adherence was generally high (range: 45-100%, with an average of 86.3%). High implementation quality of the program in the areas of student interest, student participation and involvement, classroom control, use of interactive delivery method, use of strategies to enhance student motivation, use of positive and supportive feedbacks, instructors' familiarity with the students, degree of achievement of the objectives, time management, lesson preparation, overall implementation quality, and success of implementation was also found. The present findings are consistent with those observations based on the experimental implementation phase, suggesting that the implementation quality of the Tier 1 Program (Secondary 1 Curriculum) was generally high.