Abstract: Teachers can have a significant and lasting impact on their students in the classroom. In particular, they can establish classroom practices that help students develop a positive mindset so that they embrace challenges and learn from their mistakes. However, teachers have little or no access to students over academic breaks, so how can they encourage students during these times to put forth effort, take on challenges, and stay fresh on their learning? The Keep in School Shape (KiSS) Program is a mobile intervention that embraces the growth mindset metaphor of the brain as a muscle that grows stronger with regular exercise. The KiSS Program makes “working out” easy by delivering a daily review activity to students over academic breaks via text message or email. This paper describes how various program design decisions and features communicate an even more pronounced growth mindset message to encourage students to learn from their mistakes and push themselves. Results of this observational study indicate that including features such as challenge problem hints, access to worked solutions, and confirmation checks may hold promise for how teachers can help students grow a growth mindset, even when school is not in session.