The purpose of this study is to construct a critical thinking measure that explores and evaluates how the preservice teachers develop critical thinking skills in a technology-enhanced prerequisite course in the teaching credential program at a school of education in Central California. In particular, we measured the students' critical thinking skill development through four online discussions in three sections of the CI 100 course (N=54), titled "Application of Technology in the Classroom" by creating and establishing the validity and reliability evidence of the instrument modified from an existing critical thinking rubric. The findings of the study will serve as points of reference for future course design and critical thinking assessment for online discussions.