Generating solutions for society's complex problems will require the development of a diverse workforce that is committed to technological and social innovation. In the United States, this need is being addressed by the invention education movement, a goal of which is to promote the adoption of an inventive mindset among K-12 students through outreach and out-of-school time programming that promotes habitual problem finding, creative problem solving, collaboration, and persistence (Lemelson Foundation, 2020). In this study we examined a STEM-based invention education program, Camp Invention®, for its potential as a context for inventive mindset development. Our analysis of pre- and post-camp questionnaire responses from 108 upper elementary and middle school-aged children generated a measure of inventive mindset which was stable over time but largely independent of children's identification with three STEM subjects typically encountered in school. In alignment with prior studies examining features of educational contexts that support identity development (Kaplan et al., 2014), we found that children's most preferred activities supported perceived confidence, task novelty, and task utility, and least preferred activities received lower ratings on perceived autonomy and psychological safety. We consider theoretical and practical implications for the design and evaluation of STEM-based invention education programs.