This article presents results from two studies that included ethnically and socioeconomically diverse samples totaling 4,462 children in kindergarten through third grade. Each study examined the psychometric properties 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. Both studies provided evidence that (a) individual assessment modules exhibited moderate to high internal consistency and low to moderate test-retest reliability; (b) composite assessment scores exhibited high reliability; (c) together, assessment modules demonstrated a theoretically coherent factor structure; (d) factor scores demonstrated convergent and discriminant validity; and (e) controlling for IQ and demographic characteristics, performance on the assessment modules was positively related to peer acceptance, teacher report of social skills, and multiple indicators of academic achievement, and negatively related to teacher report of problem behaviors.