The purpose of this study was to assess the impact of eighteen 11th grade high school chemistry students' prior mathematical knowledge on their understanding of certain chemical concepts (symbol, formula, and equation). It also investigated students' ideas about the meaning of plus sign, reaction sign, and the relationships between subscript, and coefficient. A combination of quantitative and qualitative methods were employed in a two-stage approach involving a preliminary study and a main study over one academic school year. The cooperating high school chemistry teacher was an active participant consultant throughout the research process. The findings indicated that about one-third of the interviewed students held common prescientific conceptions and the remainder of the students held unique concepts. The identified prescientific conceptions were common and prevalent among the students regardless of achievement level, sex, interest, age, and prior knowledge, and seemed to have different causes/sources. Based on these findings, recommendations are made and implications are suggested for high school chemistry teachers, curriculum developers, and chemistry education researchers. (Author)