Having a growth mindset has been shown to predict better academic performance in a variety of educational settings. Efforts to instill a growth mindset through educational interventions have demonstrated positive effects on academic success. However, many of the interventions previously tested are relatively time intensive and costly for some instructors at large research-intensive institutions. In this study, we find that a quick and easy mindset intervention can produce some gains in academic performance. This intervention involved no class time, little prep-work, and was easily disseminated to a 300-student Introductory Psychology lecture. Participants (N = 278) were randomly assigned to receive a growth mindset, fixed mindset, or control letter from their instructor after their first midterm exam. Nine weeks post-intervention, participants were given a manipulation check to see who read and remembered their letter's message. Of participants who passed the manipulation check (N = 86), those in the growth mindset condition outperform their fixed mindset counterparts by as much as 9%.