BackgroundResearch is needed to better understand the specific challenges for autistic learners in informal STEM learning settings. This study aimed to increase inclusion in STEM museums, with a larger goal of increasing the impact (i.e., learning and application of knowledge during and after visits) of informal STEM learning settings for autistic youth. We conducted an online parent attitudes survey with 93 parents of autistic adolescents and 53 parents of adolescents in the general population to better understand the experiences of autistic adolescents when visiting STEM-related museums. Parent responses informed professional development training for museum staff at four partner museums, which taught strategies to better support autistic learners. Then, autistic adolescents (n = 20) and their parents were randomly assigned to visit one partner and one control museum. They were asked to report their experiences through an online survey and semi-structured interviews.ResultsParticipants who completed the parent attitudes survey indicated significantly lower inclusion, engagement, and general impact of STEM museum visits among autistic adolescents compared to the general population comparison group. Parents of adolescents who visited partner and control museums reported higher STEM impact during visits to partner museums; however, parent-reported inclusion, engagement, and general impact did not differ significantly between partner and control museums. Qualitative analysis identified four themes (Spectrum of Museum Impact; Adolescent-Environment Fit; Barriers to Engagement, and Barrier Breakers), providing context for quantitative findings.ConclusionsFindings underscore the need for increased inclusion for autistic individuals in informal STEM learning environments like museums. This project demonstrated feasibility of professional development training of forward-facing staff and identified several themes that should inform future efforts to improve inclusion in informal STEM learning settings.