This study investigated the relationship of kindergarten teachers' ratings of their students' 21st century skills (college readiness skills) with students' behavioral and academic performance. Teachers rated the frequency that their students (n = 579) demonstrated persistence, curiosity, affective, and cognitive (e.g., critical thinking) behaviors within their classrooms via the Human Behavior Rating Scale: Brief (HBRS: Brief, a teacher rating scale. The relationship of the HBRS: Brief teachers' ratings was compared with data the school annually collected (behavioral ratings, academic performance, student office discipline referrals [ODRs], and absences). Hierarchical linear modeling indicated that teachers' ratings of students' persistence and cognition behaviors were significantly associated with students' academic performance. Teachers' persistence, curiosity, and externalizing affect ratings were predictive of behavioral ratings and teachers' externalizing affect ratings were significantly associated with ODRs. The results support the efficacy of investigating teacher perceptions of students' 21st century skills with kindergarteners.