As a follow-up to Horner et al., this study focuses on the internal consistency and validity of the School-wide Evaluation Tool (SET) at all school levels. Analyzing SET data from 833 elementary, 264 middle, and 93 high schools, the authors focused on (a) describing commonalities and differences in SET data across the school levels, (b) assessing the SET's internal consistency at all school levels, and (c) examining the SET's validity as the extent to which SET scores collected by external observers correlated with Team Implementation Checklist (TIC) scores reflecting internal self-assessments. Results indicated that overall, the SET performs best in elementary schools, shows less cohesion in middle and high schools, and highly correlates with TIC scores. Based on these results, the authors formulated a number of recommendations to improve the utility of SET data for research and implementation decisions across school levels and implementation phases. (Contains 9 tables and 3 figures.)