Few assessments of self-regulation for preschool-aged children have been validated for use in socioeconomically and racially/ethnically diverse populations. We address this gap by exploring the validity of the Preschool Self-Regulation Assessment -- Assessor Report (PSRA-AR), an observer report of children's global self-regulation ability, using data from a population-based sample drawn from a large and diverse school district. We found that a three factor structure - representing attention regulation, impulse control, and positive engagement - fit the data well for the entire sample. Then, using multigroup confirmatory factor analyses, we found full scalar invariance across sex and low-income status. Scalar invariance held for all but one item across Black, White, and Hispanic children. These findings suggest that the PSRA-AR is valid for use with children of diverse socioeconomic and racial/ethnic backgrounds. Moreover, the PSRA-AR was moderately correlated with direct assessments of executive function and academic ability, including early math and reading. (author abstract)