We studied how students engaged with an interactive simulation in a classroom setting and how that engagement was affected by the design of a guiding activity. Students (n = 210) completed a written activity using an interactive simulation in second semester undergraduate general chemistry recitations. The same simulation--PhET Interactive Simulations' "Acid-Base Solutions"--was used with three written activities, designated as Heavy Guidance (HG), Moderate Guidance (MG), or Light Guidance (LG). We collected mouse click data and classroom field notes to assess student engagement with each type of activity. Simulation features were characterized as "prompted" or "exploratory" based on the presence or absence of explicit guidance in the written activity to use that feature. While students in every condition were engaged with the simulation and their activity, student interaction with "exploratory" features decreased significantly when more guidance was provided (LG = 85%, MG = 68%, HG = 9%, p < 0.0005). Lighter guidance groups explored more and attended to their simulation interactions, indicated by a redraw task in the week after use. These results indicate that activity design--in terms of guidance level--can strongly influence student exploration with an interactive simulation. We discuss the implications of these results for the design of activities to accompany simulations, including how to increase student practice in scientific inquiry.