Adolescent sexual maturation is staged using Tanner criteria assessed by clinicians, parents, or adolescents. The physiology of sexual maturation is driven by gonadal hormones. We investigate Tanner stage progression as a function of increasing gonadal hormone concentration and compare performances of different raters. Fifty-six boys (mean age, 12.7 ± 1.3 years) and 52 girls (mean age, 12.0 ± 1.6 years) were seen at baseline, 6 and 12 months. Estradiol and testosterone concentrations were determined from three morning serum samples and Tanner stage by three different raters (clinician, parent, and adolescent). Results confirm that Tanner criteria reflect gonadal hormone concentrations, and clinician rating provides optimal assessment. Detailed insight about the strengths and limitations of different raters is provided, augmenting the scientific understanding of pubertal development.