Numerous studies illustrate the value of simulations or project-based learning approaches to enhance the learning of science. Simulations can help students connect across macroscopic, microscopic, and symbolic representations of scientific phenomena, while project-based learning can provide a meaningful narrative and activities for students to engage in. Despite such studies, less is known about simulation sequencing within project-based learning and how such sequencing may influence conceptual understanding. This study investigates such simulation sequencing within an online-supported project-based learning unit that focuses on a drought narrative to teach solution chemistry concepts for 10th graders (n = 72). Specifically, we compare two treatments with students randomly assigned to using a simulation before (planning treatment; n = 37) or after (reflection treatment; n = 35) the design of desalination units. This quasi-experimental study includes a pre/post conceptual test, embedded conceptual measures, a student questionnaire, a teacher interview, and classroom observations. Results show significant pre/post gains for all students on solution chemistry concepts. Findings show no overall difference between the two treatments. Student and teacher comments, and classroom observations illustrate affordances and constraints for teaching solution chemistry concepts through a technology-supported project and point to future directions for iteration. We discuss the implications of this work for future technology-supported projects and science education.