The interest in computational thinking development at pre-university education stage is increasing. In this study, a meta-analysis was conducted to address two main objectives: (a) to analyze the effectiveness of empirical interventions in K-12 education for the development of Computational Thinking (CT); and (b) to identify and evaluate the variables that influences the effectiveness of the interventions. The analysis was especially focused on the intra-group effect sizes. Interventions show large effect size in the development of CT in the comparison between pre- and post-tests (g = 1.044). Among the different types of interventions, programming is the most efficient learning tool.