Teacher training in computational thinking (CT) is becoming more and more important, as many countries are introducing CT at all K-12 school levels. Introductory programming courses are known to be difficult, and some studies suggest they foster an entity theory of intelligence (fixed mindset), reinforcing the idea that only some people have so-called "geek gene". This is particularly dangerous if thought by future primary school teachers. We analyzed the effects of an introductory course about computational thinking and creative computing with Scratch, and observed a statistically significant increase of pre-service teachers' growth mindset while observing a statistically significant decrease in their computer anxiety. The structure of the course is detailed, with particular emphasis on some characteristics that may have determined growth mindset increase. Limitations of this exploratory study are discussed, and future work is depicted.