Student success in introductory computing course continues to be a major challenge. Though there has been much research and innovation in recent years to help reduce high failure rates, a substantial population of students still struggle in a typical CS1 course. In this paper we create an argument of validity of the Placement Skills Inventory (PSIv1). The goal of the PSIv1 is to help advise and place students into an appropriate introductory computing course. While placement exams have been developed in the past, the goal of PSIv1 is to differentiate students who will be successful in a CS1 course and those that would be better served taking a CS0 course as their first computing course. In contrast, traditional placement exams have focused on differentiating students between CS1/CS2. The PSIv1 is a combination of two instruments, the Computational Thinking Concepts and Skills Test and the Second Computer Science 1 Exam Revised Version 2. These two instruments measure students’ computation thinking skills and prior programming knowledge respectively. The PSIv1 was administered to all students enrolled in either a CS0 or CS1 during the first two weeks of the semester. We use Item Response Theory to create an argument of validity of the PSIv1 and look at differences in scores on the PSIv1 based on if a student passed or failed a CS0 and CS1 course. We then used the results to create an advising strategy and criteria to help students decided if they should enroll in a CS0 or CS1 course.