In many parts of the world, newly hired science teachers' practices are developing in a complex policy environment. However, little is known about how newly hired science teachers' practices are enacted throughout a cycle of instruction and how these practices can be influenced by macro-, meso-, and micro-policies. Knowing how policies impact practice can result in better policies or better support for certain policies in order to enhance the instruction of newly hired teachers. This comparative study investigated how 12 newly hired science teachers at sites in South Africa (SA) and the United States (US) progressed through an instructional cycle of planning, teaching, and reflection. The qualitative data were analysed through beginning teacher competency frameworks, the cycle of instruction, and institutional theory. Data analysis revealed prevailing areas of practice and connections to levels of policy within the instructional cycle phases. There were some differences between the SA and US teachers and among first-, second-, and third-year teachers. More importantly, this study indicates that newly hired teachers are susceptible to micro-policies and are progressively developing their practice. It also shows the importance of meso-level connectors. It suggests that teacher educators and policy makers must consider how to prepare and support newly hired science teachers to achieve the shared global visions of science teaching.