This research study investigated conceptions about buoyancy held by 55 elementary preservice teachers enrolled in a science methods course who participated in an instructional intervention designed to increase their knowledge about buoyancy. Pre- and post-concept maps were analyzed using a paired sample t test and thematic analysis was used to interpret narratives, drawings, and interview data. There was a statistically significant difference (t = -3.504, p = 0.001) in the total number of scientifically correct concepts for the pre-concept maps (M = 0.51, SD = 0.879) and post-concept maps (M = 1.25, SD = 1.542). The total number of accurate propositions increased between the pre- and post-concept maps. The drawings revealed that most participants (66%) had alternative conceptions about how gravity is related to buoyancy and the role it plays in floating and sinking. Data from the interviews triangulated with other data sources that showed gains in scientific conceptions such as opposing forces (53%) and surface area (33%), while documenting the persistence of serious alternative conceptions about floating and sinking (49%), the key role of fluid density (56%), and density of an object (62%).