Informal learning experiences have become increasingly effective in enhancing self-efficacy and interest in the fields of science, technology, engineering, and mathematics (STEM).This study investigated the impact of access to informal STEM learning experiences on student self-efficacy and interest in STEM before and after participating in the 2018 See Blue See STEM Summer Experience. Pre-survey results indicated that middle school students who had previous access to informal STEM learning experiences are 3.21 times as likely to demonstrate high self-efficacy in STEM as those who had no previous access. After engaging in the 2018 summer experience, post-survey results showed a statistically significant increase in student self-efficacy in STEM and indicated that students who had previous access to informal STEM learning experiences are 4.13 times as likely to manifest interest in STEM as those who had no previous access. These results suggest that increasing exposure to informal STEM learning experiences enhances both self-efficacy and interest in STEM.