Concerns about inadequate development of subject expertise for American elementary school teachers have been well documented. There are many exceptions to this narrative, and there are many exemplary U.S. teacher preparation programs. However, it is clear that, overall, the preparation of elementary teachers in the United States in key subject areas has been inadequate. So, what are systems that have high-performing learning outcomes in key subjects doing to ensure quality teaching in math, science and literacy? This report analyses whether and how high-performing systems (specifically those in jurisdictions of Japan, Finland, Hong Kong, and Shanghai) have supported the subject expertise of their elementary school teachers. The findings highlight how different parts of these systems constantly reinforce the development of deep subject expertise in their elementary teachers. For example, these systems have: (1) Teachers selected for the specific knowledge and skills that make an effective elementary teacher; (2) Initial teacher education that is focused on how to teach the elementary school curriculum; (3) Instructional supports which develop deep subject expertise in teachers; (4) Professional development and mentoring from teacher subject experts who have been promoted to these positions because of both their subject expertise and ability to help other teachers; and (5) Recognition and promotion for all teachers based on teacher subject expertise, encompassing school-based research and their ability to develop other subject teachers.