This study examined the relationship of teachers' ratings of students' 21st century skills (i.e., persistence, curiosity, externalizing and internalizing affect, and cognition) via the Human Behavior Rating Scale: Brief (HBRS: Brief; Eaves & Woods-Groves, 2011) with student performance. Midwestern K-11 teachers (n = 96) rated students (n = 1,689) via the HBRS: Brief and the Strengths and Difficulties Questionnaire (SDQ; Goodman, 1997). Students' academic (i.e., standardized tests) and behavioral (i.e., office discipline referrals [ODRs] and absences) performance was compared with HBRS: Brief ratings. Hierarchical linear modeling revealed that teachers' ratings of students' 21st century skills were related to the following: (a) Persistence with SDQ conduct problems, academic performance, and absences; (b) curiosity with SDQ emotional symptoms; (c) externalizing affect with SDQ conduct problems, academic performance, and ODRs; (d) internalizing affect with SDQ emotional symptoms and academic performance, and (e) cognition with academics.