[This paper is part of the Focused Collection on Astronomy Education Research.] We examined teachers' spatial-scientific reasoning and the alternative conceptions they held regarding Earth-space content. While participating in a professional development (PD) workshop, teachers engaged in an integrated mathematics and science project-based unit designed to foster spatial reasoning and improve lunar-related conceptual understanding. The Purdue Spatial Visualization Test-Rotation (PSVT-Rot) and the Lunar Phases Concept Inventory (LPCI) were used to assess understanding. We found the teachers held similar alternative conceptions as their students. Moreover, we discovered that teachers had limited understanding of the Earth-Moon-Sun scale, motions, and geometric configurations. To determine how teachers' spatial-scientific confidence and ability translated to their classroom practice, we videotaped and analyzed instruction conducted by 6 teachers on an Earth-space lesson. Two teachers with the highest spatial-scientific confidence and ability had students achieving significant learning outcomes on both the PSVT-Rot and the LPCI.