© WIETE 2019 The computing professional skills assessment (CPSA) is a way to assess the non-technical student learning outcomes for the Accreditation Board for Engineering and Technology (ABET) in the discipline of computing. These outcomes, also known as 21st Century, transferable or general education learning outcomes are recognised as essential for employment, but they have proven a challenge to assess in a direct and integrated manner. The CPSA overcomes this challenge with its scenario-based, small group, on-line discussion, where faculty raters assess the discussion transcripts according to the criteria presented in the six-part CPSA rubric. The method has been used with more than 600 computing students over a five-year period. Here, the authors present results on the reliability and validity of the instrument. Reliability was examined through evidence-based rater discussions and analysis of interrater reliability. Validity was examined through construct, content, criterion related and concurrent forms of validity. The results provide evidence that the instrument is reliable and valid.