The Inclusive Assessment of Computational Thinking (CT) designed for accessibility and learner variability was studied in over 50 classes in US schools (grades 3-8). The validation studies of IACT sampled thousands of students to establish IACT's construct and concurrent validity as well as test-retest reliability. IACT items for each CT practice were correlated to examine construct validity. The CT pre-measures were correlated with post-measures to examine test-retest reliability. The CT post-measures were correlated with external measures to examine concurrent validity. IACT studies showed moderate evidence of test-retest reliability and concurrent validity and low to moderate evidence of construct validity for an aggregated measure of CT, but weaker validity and reliability evidence for individual CT practices. These findings were similar for students with and without IEPs or 504s. IACT is the first CT tool for grades 3-8 that has been validated in a large-scale study among students with and without IEPs or 504s. While improvements are needed for stronger validity, it is a promising start.