Parents (n = 11,845) completed the Modified Checklist for Autism in Toddlers (or its latest revision) at pediatric visits. Using sociodemographic predictors of maternal education and race, binary logistic regressions were utilized to examine differences in autism screening, diagnostic evaluation participation rates and outcomes, and reasons for non-participation. Families of lower maternal education and racial minorities exhibited inflated initial screen positive rates and lower participation at Follow-Up, although not at the evaluation. Economic challenges, such as invalid phone numbers, were identified as barriers to reaching these families. Families of higher education and White race were more likely to decline participation in evaluation. Results suggest the need for increased public education about childhood development to enhance awareness, reduce stigma, and streamline screening.