This study aimed at describing the effectiveness of: (1) the context of Teachers Working Group program viewed from the relevance between the goals and objectives of its program to the needs and problems of increasing the teachers’ professionalism; (2) input (feed-back) of Teachers Working Group program from the conformity of participating teachers characteristics, work programs, and its organizational capabilities in achieving program objectives based on the development standards; (3) the process of Teachers Working Group program implementation from the compatibility of tutor performance, member activity, infra-structure utilization, and its performance management based on the development standard; and (4) the effectiveness of Teachers Working Group program for improving the participating teachers’ professionalism and their attitudes toward the program. This is an evaluational research by which the model included evaluation of Context, Input, Process, and Product (CIPP) developed by Stuffle beam. The study was conducted in Cluster 1 and Cluster 4 of the Teachers Working Group in Blimbing, Malang, East Java, Indonesia, in January-April 2016. The informants were members of the board and some participating teachers, and coaches in both clusters. Data were collected by observation, interview, and documentation. The data were analyzed by using Yin model consisting of five stages, namely compiling, disassembling, reassembling, interpreting, and concluding. The findings indicated that (1) the relevance between the goals and objectives of the program to the needs and problems of teachers’ professionalism improvement and the Teachers Working Group context in both groups were sufficiently effective to achieve the program objectives. The component of cluster 1 context was more effective than that of cluster 4. The objectives, the needs of teachers, and work programs of group 1 were more relevant than those of group 4; (2) In terms of the teachers’ interest to program and teachers’ needs of learning management, training programs, and capabilities of tutors and administrators in both groups, the input component of cluster 1 was quite effective, while cluster 4 was less effective; (3) In terms of compatibility of tutor performance, member activity, infrastructure utilization, and the group management performance, the program implementation in both groups were equally effective; and (4) In terms of the benefits of the program for the improvement of teacher is professionalism and teacher is positive attitude towards the program in both groups, the implementation of the program in both groups was classified quite effective.