The Chronbach's Alpha of the TSAS was computed in 2014 and shows very high internal consistency reliability (r= .962). As stated well in Wikipedia:
…internal consistency is typically a measure based on the correlations between different items on the same test (or the same subscale on a larger test). It measures whether several items that propose to measure the same general construct produce similar scores. For example, if a respondent expressed agreement with the statements "I like to ride bicycles" and "I've enjoyed riding bicycles in the past", and disagreement with the statement "I hate bicycles", this would be indicative of good internal consistency of the test.
The Center for Positive Practices designed the TSAS questionnaire and computed the results and has no tangible stake in your school or district results. The TSAS, like NMTEACH, has yet to be fully studied for internal and external validity, and revisions to NMTEACH are presently in progress so we deferring to that process before making further assumptions.
Nonetheless, we believe that the TSAS statistical results are the truest picture we can get because a) the responses come directly from teachers, b) the questionnaire is anonymous, c) there is no offer of reward or punishment dependent on the results, and d) we know from self-efficacy theory (Bandura, et al. 1977-2006) that the most accurate assessment of one's personal capabilities to successfully perform designated tasks most often comes from the respondent her/himself. That doesn't mean, however, that we ever fully exert the full potential of our capabilities; just that could always do more if the conditions were right.