Physical computing, making, tinkering and Computational Thinking (CT) are frequently applied to promote Computer Science (CS) and attract the attention of young people. In recent years, STEM (Science, Technology, Engineering, and Mathematics) education has received considerable support from schools, parents, and communities. The combination of physical computing with STEM education can improve CT as part of CS or informatics/computing education and can be considered as an essential skill for the workforce of the 21st century. Physical computing helps children build connections between the real world and programming, while giving them something exciting to focus on. The goal of this study is to demonstrate how a summer school on physical computing and STEM education including CT contributes to shaping girls’ attitudes and their acceptance of technology. To examine how the technology acceptance factors are related to the girls’ behavioural intention and attitude change towards the use of microcontrollers, an adaptation of the Unified Theory of Acceptance and Use of Technology (UTAUT) was applied. The survey was conducted with 21 girls, 11 to 15 years old, both before and after summer school. The results showed that carefully planned activities on mini-projects with purposeful support of lecturers reduce the technological anxiety and contributes to the girls’ intention to use technology in the future. The implications of these results can be used to develop various supporting physical computing activities in the school community. The methodology, examples and real stories of success of girls in computing help teachers to promote CS education in schools.