This study aims to: 1) describe the needs of junior high school teachers and students in learning mathematics; 2) obtain comprehensive information in designing cooperative learning models that can improve junior high school students' mathematical generalization abilities; 3) produce cooperative learning models in improving the mathematical generalization abilities of junior high school students that are valid, practical, and effective. This research is research and development by adopting the Plomp model design which consists of five phases, namely initial investigation, design, realization/construction phase, test phase, evaluation, and revision and implementation phase. Data collection was carried out using several instruments in the form of needs analysis questionnaires, validation questionnaires, observation sheets, teacher response questionnaires, and tests of mathematical generalization ability. The data collected was then analyzed using qualitative and quantitative methods. The results of the study show that: (1) Both teachers and junior high school students really need to develop learning models that can improve students' mathematical generalization abilities; (2) The cooperative learning model can improve the mathematical generalization ability of junior high school students which includes 3 stages of learning, namely the active stage, the collaborative stage, and the inductive stage; and (3) The results of the validation test show that the model book and learning tools are declared valid based on the judgment of the experts. Furthermore, the results of the practicality test also state that the model is practical based on the results of observations of the implementation of learning, learning management, and teacher response questionnaires. While the results of the effectiveness test through the n-gain test from the pretest and posttest data indicate that this learning model is declared effective for increasing the mathematical generalization abilities of junior high school students.