This study investigated young children's computational thinking (CT) development by integrating ScratchJr into a programming curriculum. Twelve third graders (six males and six females) voluntarily participated in an experiment-based computer class conducted at a public elementary school in Taiwan. This study adopted a case study methodology to investigate research questions in one specific case (8-week CT educational training). A one-group quasi-experimental pretest and posttest design with the support of qualitative observation was used to examine four research topics: CT competence progress, programming behaviors in a CT framework, factors influencing CT competence, and learning responses to CT training. The quantitative results indicated that students immersing in weekly programming projects significantly improved in terms of their CT competence, which was mostly retained 1 month after completion of the class. The programming behaviors indicated that students' CT concepts (sequence, event, and parallelism) and practice (testing and debugging as well as reusing and remixing) significantly improved. Moreover, parents' active involvement in take-home assignments influenced students' long-term CT competence retention. The qualitative results indicated that students enjoyed using tablet computers to learn ScratchJr programming and demonstrated various leaning behaviors in a three-stage instructional design model.