The intent of national efforts to frame science education standards is to promote students' development of scientific practices and conceptual understanding for their future role as scientifically literate citizens (NRC 2012). A guiding principle of science education reform is that all students receive equitable opportunities to engage in rigorous science learning. Yet, implementation of science education reform depends on teachers' instructional decisions. In urban schools serving students primarily from poor, diverse communities, teachers typically face obstacles in providing reform-based science due to limited resources and accountability pressures, as well as a culture of teacher-directed pedagogy, and deficit views of students. The purpose of this qualitative research was to study two white, fourth grade teachers from high-poverty urban schools, who were identified as transforming their science teaching and to investigate how their beliefs, knowledge bases, and resources shaped their planning for reform-based science. Using the Shavelson and Stern's decision model for teacher planning to analyze evidence gathered from interviews, documents, planning meetings, and lesson observations, the findings indicated their planning for scientific practices was influenced by the type and extent of professional development each received, each teacher's beliefs about their students and their background, and the mission and learning environment each teacher envisioned for the reform to serve their students. The results provided specific insights into factors that impacted their planning in high-poverty urban schools and indicated considerations for those in similar contexts to promote teachers' planning for equitable science learning opportunities by all students.