Computational thinking (CT) is increasingly integrated into education, promoting problem-solving skills essential for the 21st century. However, little is known about how teachers assess CT in K-12 classrooms. This qualitative study explores elementary teachers' approaches to CT assessment after professional development in integrating CT into core subjects. Interviews with eleven teachers revealed key findings regarding what, how, and why they assess CT. Teachers frequently assessed debugging, decomposition, and, to a lesser extent, abstraction and patterns. They used observations and student explanations to gauge CT processes and valued real-life applications of CT as evidence of learning. However, there was variation in teachers' beliefs about what constitutes assessment, with some favoring project-based methods and others seeing assessment as observing students' CT in action. This study highlights the challenges and opportunities in developing robust CT assessment practices in elementary education.