This paper describes methods and findings from student cognitive labs, teacher cognitive labs, and test administration observations as evidence evaluated in a validity argument for a computer-based alternate assessment for students with significant cognitive disabilities. Validity of score interpretations and uses for alternate assessments based on alternate academic achievement standards (AA-AAAS) for students with the most significant cognitive disabilities require nontraditional sources of evidence about student-item interactions and the influences teachers have on those interactions. Our findings provide evidence that the assessment has been designed so students can show what they know and can do on multiple choice, technology-enhanced, and teacher administered item types and that teachers administer the assessments in a way that allows students to respond as intended. We conclude with a discussion on how the findings inform future test development, limitations, and implications for the use of these research methods for gathering validity evidence for an AA-AAAS.