Proficiency in Computational Thinking (CT) and related abilities are increasingly important to success in our technologically oriented society. While there are various means of measuring CT skills in older children and adolescents, there are currently no validated instruments for this purpose applicable to early elementary school children. We have developed a pilot CT assessment tool called TACTIC-KIBO for children as young as 4 years of age designed to assist educators and researchers. Our approach employs KIBO, a robotics platform that uses tangible blocks instead of a screen to engage children in playful programming activities. TACTIC-KIBO probes seven domains of CT and classifies four levels of proficiency. In this chapter, we describe our initial experiences in assessment and discuss possible future directions and implications for education and research.