Abstract. This research study reports on the use of concept maps as an assessment tool to investigate elementary pre-service teacher knowledge about dissolving. Propositions from pre/post concept maps were scored using the total proposition accuracy scoring technique (TPA) and were also used to classify concepts as scientific or spontaneous using Vygotsky’s theory of concept development. Vygotsky (1986) described spontaneous concepts as un-unified and employing concrete, factual groupings, while scientific concepts are organized hierarchically and have a system. After the instructional intervention, statistically significant improvement was shown on a paired sample t-test (t =-4.154, p<.001) and many spontaneous concepts which appeared on the pre-concept maps, were either reduced or eliminated (i.e., disappearing and melting). Although medium statistically significant gains were noted for the t-test, these findings suggest that the elementary pre-service teacher science content knowledge about dissolving is weak as the average TPA score was less than two accurate propositions (n=49) and many teachers continued to hold the same misconceptions as reported for K-12 students in previous studies (Calik & Ayas, 2005; Kind, 2004; Kikas, 2001; Ebenezer & Erikson, 1996). This research also suggests the teachers have well-developed idiosyncratic conceptions about dissolving that will take considerable time and effort to reduce and/or eliminate. Recommendations to improve the content knowledge for elementary pre-service teachers include: adding a non-majors chemistry course, focusing on the particulate nature of matter during methods course work, and using screening practices to eliminate pre-service teachers who display weak science knowledge about the subjects they will teach to children.