Computer science (CS) has become a critical part of K-12 education worldwide. Computational thinking (CT) skills are a key set of competencies in CS education that can solve problems and use computational design to create useful solutions. However, preservice and in-service teachers are not fully prepared to integrate CS and CT into their curricula. Furthermore, there are limited special topic courses and educational research on how to facilitate in-service teachers' professional learning of CS and CT, as well as their content specific integration. Therefore, this study investigated in service teachers' perceptions and development of CT skills in an online graduate emerging technologies course. Theoretically framed by the four cornerstones of CT (i.e., abstraction, algorithms, decomposition, and pattern recognition), participants perceived that they increased their CT problem-solving and creativity skills but decreased their collaborative learning and critical thinking skills. Additionally, teachers increased their CT test scores after taking the course. Most teachers used CT terminology correctly (i.e., algorithms and decomposition). However, only 59% correctly described abstraction and pattern recognition, while most teachers did not mention debugging. The authors call on teacher educators to address in-service teachers' CS knowledge gaps, increase their CT skills, and select appropriate strategies for CT professional learning.