In this study we examined the relationship of students' 21st century skills with their academic and behavioral outcomes. We investigated K-12 teachers' (n = 150) judgment of students' (n = 3,108) use of 21st century skills (i.e., persistence, curiosity, affect, and cognition behaviors) via a Likert-type rating scale. We compared teachers' ratings with students' academic and behavioral outcomes in a southeastern school district. We used Hierarchical Linear Modeling with length of teacher acquaintance with the student as the nesting variable. Teacher ratings for students' low instances of persistence behaviors and high instances of externalizing affect behaviors were predictive of a higher probability of student office discipline referrals. We found a positive correlation for teachers' ratings of students' cognition behaviors and their reading, mathematics, and science outcomes. Teachers' student length of acquaintance was significant for academic outcomes. Results indicated a predictive relationship with teachers' judgment of students' 21st century skills and student outcomes.