Many arguments are used to advocate for the introduction of Computer Science (CS) / Computational Thinking / "coding" in K-12 education. Growth mindset theory (GM) is also becoming very popular among educators and researchers. Some claims stating that studying CS can foster a GM have emerged. However, educational research shows that transfer of competences is hard. Very little research has been conducted on the relationship between GM and CS learning, with conflicting results. We measured some indicators (e.g., mindset, computer science mindset) at the beginning and the end of a high school year in five different classes: three CS oriented , one Chemistry oriented, and one Transportation&Logistics oriented. In one of the CS oriented classes, we did a very brief GM intervention. At the end of the school year, none of the classes showed a statistically significant change in their mindset. Interestingly , non-CS oriented classes showed a significant decrease in their computer science growth mindset. In the intervention class, students suggested, to stimulate a GM, the need for activities that are more creative, engaging, and related to the real world and their interests.