The National Longitudinal Study of Adolescent Health's School Connectedness Scale (SCS) has been widely used in psychological, public health, and education research, but has undergone limited psychometric analysis. This study used the responses of 500,800 junior and senior high school students who completed the biennial California Healthy Kids Survey, which includes the SCS. The results supported the use of the SCS as a unidimensional measure and showed that it has acceptable reliability (alpha = 0.82 to 0.88) and concurrent validity (r = 0.44 to 0.55) across 18 sociocultural groups. A series of multiple group analyses confirmed configural, metric, and scalar equivalence across groups. The SCS shows promise as measurement instrument for school psychologists; however, further research is needed to examine its underlying latent school connectedness construct. (Contains 3 tables.)