This study aims to improve the mathematical communication and learning outcomes of junior high school students by implementing the CORE (Connecting, Organizing, Reflecting, and Extending) learning model. Mathematical communication refers to five aspects: representation, listening, reading, discussion and writing. This type of research is a classroom action research conducted at SMP Negeri 1 Jombang in class VIII and carried out in 2 cycles. The results showed that the mathematical communication in the first cycle, the percentage of the representation aspect was 57.81% in the medium category, while the second cycle was 82.81% in the high category. The listening aspect in the first cycle was 56,25% in the medium category, and in the second cycle, it was 78,13% in the high category. The reading aspect in the first cycle is 50% in the medium category, and in the second cycle, it is 87.5% in the high category. The discussion aspect in the first cycle was 48.38% in the low category, and in the second cycle, it was 84.38% in the medium category. The writing aspect in the first cycle was 62.5% in the medium category, and in the second cycle, it was 92.19% in the high category. The average learning outcome in the first cycle is 68.69 and in the second cycle is 86. Therefore, the application of the CORE model is very effective in improving mathematical communication skills and learning outcomes. Teachers are expected to modify and integrate the CORE model with STEM and think critically and creatively.