This study aimed to conduct an in-depth evaluation of the activity-based computational thinking teaching practices performed to improve computational thinking and teaching skills of the basic education teachers. Based on the aim of the study, the case study design, one of the qualitative research methods, was selected. As a result of the collaborative work of five experts, a 20-hour education program built on two core competencies, four sub-competencies and eight thinking skills was implemented. The participants were 40 teachers, 20 of whom were classroom teachers and 20 of whom were pre-school teachers. Data were collected from three different sources using five data collection tools in order to conduct an in-depth analysis of the practices. Quantitative and qualitative data collection tools were used in a combined fashion in the research. The data were analyzed through content analysis and non-parametric analyses. Our findings revealed that thanks to the teaching practices performed, classroom teachers had significantly higher problem solving, diverse thinking, algorithmic thinking, and computational thinking total scores, while preschool teachers achieved significantly higher total scores in algorithmic thinking skills and computational thinking. It was observed that the participants defined computational thinking on the basis of 18 different thinking skills. The explanations of the participants about the functions of computational thinking skills were grouped under seven categories. When the principles that should be considered in the teaching of computational thinking skills were examined, it was seen that the need for utilizing scaffolds was stated the most.