Health literacy can help explain health inequalities in childhood and adolescence. However, suitable instruments for assessing health literacy in this age group are rare, especially in the German-speaking countries. One economical measure is the 10-item Health Literacy in School-Aged Children (HLSAC) scale, developed and reviewed as part of the WHO Child and Adolescent Health Study (HBSC, Health Behavior in School-Aged Children). In the present study, we tested dimensionality, measurement invariance, and associations with health-related measures of the German version of the scale (HLSAC–German), using data from the 2018 national German HBSC study (N = 4,347 students aged 11, 13, and 15 years). We also tested HLSAC–German with 11-year-olds, representing an expansion of the original scale. Exploratory and confirmatory factor analyses consistently demonstrated the unidimensionality of the scale (α = .88). Complete scalar measurement invariance was found for sex and partial scalar measurement invariance for age groups and school type, allowing for the comparison of means. Associations with indicators of health and health behavior further demonstrate the construct validity of the scale. The analyses show that the scale is suitable for the economic measurement of a general factor of health literacy in 11- as well as in 13- and 15-year-olds.