With an abundance of datasets of standardized test score data, researchers and education policymakers run the risk of focusing exclusively on the measurement of cognitive outcomes in key academic subjects such as math and reading at the expense of important non-cognitive outcomes. We use behavioral measures of conscientiousness, perseverance, and delay of gratification as well as a self-reported measure of student grit--defined as student perseverance and passion for long-term goals--to assess the non-cognitive skills of 174 16- to 18-year-old students attending a residential public high school in Arkansas, United States. Analysis shows that 11th grade students (16- to 17-year-olds) rate themselves lower on self-reported grit but outperform their 12th grade counterparts (17- to 18-year-olds) on behavioral measures of persistence, delay of gratification, and conscientiousness. These findings point to the strengths and limitations of existing tools for measuring non-cognitive skills and the need for more measures to be developed and tested with diverse populations.