The purpose of this study was to evaluate the psychometric properties and measurement invariance of a web-based, self-administered battery of assessments of social-emotional comprehension called "SELweb." Assessment modules measured children's ability to read facial expressions, infer others' perspectives, solve social problems, delay gratification, and tolerate frustration. In an ethnically and socioeconomically diverse sample of 4,419 children in kindergarten through third grade who completed SELweb: (a) scores from assessment modules exhibited moderate to high internal consistency and moderate 6-month temporal stability; (b) composite assessment scores exhibited high reliability; and (c) assessment module scores fit a theoretically coherent four-factor model that includes factors reflecting emotion recognition, social perspective-taking, social problem-solving, and self-control. In addition, the present study supports configural and metric invariance across time, sex, and ethnicity. Analyses suggest partial scalar invariance across time, sex, and, to a lesser degree, ethnicity. [This article was published in "Journal of Psychoeducational Assessment" (EJ1217501).]