Education research frequently calls for theory-building work to better explain the mechanisms of how people learn. This talk discusses two theories developed based on a synthesis of work across multiple education-related fields to explain phenomena frequently seen in STEM education. The first theory, Spatial Encoding Strategy theory, proposes a mechanism to explain how spatial skill training improves generalized problem solving while other forms of brain training produce only localized results. It draws upon work in discipline-based education, cognitive psychology, neuroscience, and learning sciences. The second theory, Multiple Conceptions theory, proposes a mechanism to explain how both direct instruction and constructivist instructional approaches can be designed to guarantee successful results. It draws upon instructional approaches from various STEM fields and educational psychology.