The objectives of the study are: 1) to describe the design of the Cooperative Translation Based Learning model to improve students’ achievement in class XII; 2) to assess the feasibility of the Cooperative Translation Based Learning model to improve students’ achievement in class XII; and 3) to measure the effectiveness of the Cooperative Translation Based Learning model to improve students’ achievement in class XII. The type of research is Research and Development (R&D). The data of this research are English learning activities in class XII of SMKIT Nur Hasan Boarding School; data on the achievement of learning English in class XII of SMKIT Nur Hasan Boarding School. Data were collected through tests, observations, and questionnaires. Data were analyzed using inferential analysis and qualitative analysis. The feasibility test for developing the Cooperative Translation Based Learning model shows 96.7% with very practical criteria. Under the practicality criteria in the large group trial, the learning module “Cooperative Translation Based Learning for Writing Skill Grade XII” in learning to write English Business letters is stated to be very practical and feasible. The effectiveness test of the Cooperative Translation Based Learning model shows that the output of the Paired Samples Test has a Sig. (2-tailed) is 0.000 < 0.05; therefore, H0 is rejected and H1 is accepted. It can be concluded that there is a difference in the average value of learning outcomes between pre-test and post-test results. Therefore, developing the learning module “Cooperative Translation Based Learning for Writing Skill Grade XII” can improve writing learning skills.