In the last years, a growing trend in different educational contexts focused on Computational Thinking (CT) skills acquisition for both in-service teachers and students. But very low attention has been paid to pre-service teachers' education in regards to CT skills. To solve this issue, an empirical experimentation has been carried out with141 Italian pre-service teachers, that attended at a programming course, with the following aims: 1) provide them the main coding concepts by using Scratch 2.0; 2) offer practical advice on how to design educational applications (apps) to be applied into school context; 3) assess their apps by applying an already existing methodology, useful to give them feedback on their programming expertise and CT skills. Empirical findings showed that most of the participants achieved a medium-high level of CT skills, combining both design and programming skills in their school internship. Moreover, they reported a sense of greater self-esteem in teaching practice and a great emotional response from kids.