This work in progress paper analyzes disciplinary teachers' self-efficacy beliefs in Computational Thinking (CT) during a professional development program on (CT).The increasing number of professional development programs to promote the integration of CT into the curricula brings the challenge of understanding how to effectively assess them.The research team designed, implemented, and assessed a 20-hour professional development program to incorporate computational practices into disciplinary learning environments at the K-12 level in Colombia.In total, 101 in-service teachers from Colombian public middle and high schools participated in this program.We used the learning progression use-modify-create as the pedagogical framework to scaffold participants' learning process.The participating teachers completed a pretest and a post-test regarding their experience in the program, their self-efficacy beliefs in CT, and their understanding of CT concepts.As a final project of the program, the participating teachers presented a lesson plan to integrate computational thinking skills into their disciplinary courses.This lesson plan was assessed using a rubric including criteria such as the context, the learning outcomes, the assessment strategy, the pedagogical strategies, and the alignment among these components.