There has been a global emphasis in developing the STEM workforce over the last several decades. Spatial thinking ability is a strong predictor of success in STEM (Wai et al., 2009; Shea et al., 2001). Spatial thinking involves a variety of specific spatial skills that incorporate a range of spatial concepts, different types of spatial representations, and transformations through time and space (NRC, 2006). Spatial thinking typically is not formally taught in STEM courses but is often assumed to either already exist in the minds of students when they are admitted into a program or intuitively develop as they progress through their coursework (Gold et al., 2018). Our investigation sought to characterize aspects of spatial thinking instruction in undergraduate geology courses and to measure how students' spatial skills evolved as they progressed through the geology curriculum. We collected over 175 hours of observational data from 6 courses across the undergraduate geology curriculum. We assessed students' spatial thinking performance via an aggregate spatial thinking skill pre- and post-test. We will describe the results from these two data strands and compare spatial thinking instruction (observations) to students' spatial thinking gains in individual undergraduate geology courses and across the curriculum. Preliminary analyses suggest that the gains in specific spatial thinking skills correspond with instruction that places an explicit or implicit emphasis on these skills. While this study focuses on spatial thinking in geology courses, the study design could be applied to assessing the incorporation of other skills in many disciplines.