Mathematics teachers' knowledge for teaching mathematics has been broadly studied in recent years, and many theoretical frameworks and instruments have been created to measure and improve knowledge and competencies to teach mathematics. The knowledge gained from these studies has been crucial in understanding and determining what mathematics teachers should learn. In Costa Rica, there is a lack of regulations regarding the training that mathematics teachers receive and the knowledge and competencies they acquire in the different teacher education programs. This study investigates the knowledge for teaching mathematics of Costa Rican preservice teachers using the Teacher Education and Development Study in Mathematics (TEDS-M) instrument to identify strengths and weaknesses in their training. A mixed-method analysis of the responses of 79 participants revealed that they were well prepared for cognitive application skills but showed weaknesses in the development of reasoning skills. Additionally, the solutions highlighted significant deficiencies in participants' monitoring of their own work and in the ability to provide feedback on students' work. We hope that our findings could inform universities and policy makers to improve the quality of teacher education programs.