Discrete-trials teaching (DTT) is a frequently used method for implementing Applied Behavior Analysis treatment with children with autism. Fazzio, Arnal, and Martin (2007) developed a 21-component checklist, the Discrete-Trials Teaching Evaluation Form (DTTEF), for assessing instructors conducting DTT. In Phase 1 of this research, three experts on DTT rated all 21 components of the DTTEF as very important, demonstrating its high face validity. In Phase 2, the DTTEF had high interobserver reliability for live scoring of trainees' DTT performances, and it differentiated between the DTT performances of trainees before and after receiving instruction in applying DTT. In Phase 3, the DTTEF evaluations of the DTT performances of trainees in Phase 2 compared favorably to ratings of video clips of those performances by DTT experts, demonstrating high concurrent validity. (Contains 2 tables and 1 figure.)