The purpose of this study was to examine how learners' problem-solving approaches and success changed from high school to graduate school. This case study included 15 participants who were purposefully selected regarding their grade levels. To examine the development, we asked three algorithmic questions and three problems, which were different from each other regarding the data given and the context provided by stoichiometry. The data were collected through a think aloud protocols. The participants were also requested to take notes, write equations, and make calculations. Deductive data analysis was conducted. Results showed that the participants were able to solve the algorithmic questions to some extent. However, all participants had some difficulty in solving the problems. Most of the participants did not use supportive approaches to solve the problems. Implications for chemistry teaching provided in light of the results.