Abstract: Due to the rapid change in technology and information dissemination, the qualities and skills employers and colleges demand in the 21st century have changed. To help higher education institutions and workforce to identify and measure their prospective students and employees’ skills respectively, we designed an instrument for secondary grade students to self-assess their 21st century skills. After successful piloting, validation of the final instrument was done with 282 high school students from a public high school in Texas. We utilized exploratory factor analysis and investigated construct validity for the instrument using principal axis factoring with Promax rotation and Kaiser normalization. We found that the original 48 items developed for the instrument were loading the four factors as theorized in our model. Finally, confirmatory factor analysis (CFA) models for four scales were separately investigated. Maximum likelihood estimation method was used for all analyses though Mplus8.2 (Muthén & Muthén, 1998-2017). We came up with 5 factors and 43 items. Researchers, K-12 educators, postsecondary educators, and employers may benefit from the development of this instrument.