In this paper we report the work that jeKnowledge (Júnior Empresa da Faculdade de Ciências e Tecnologias da Universidade de Coimbra), a student-led initiative, has done in the ‘jeKnowledge academy’ courses to actively engage Portuguese high-school students in STEM education through hands-on projects based on the low-cost Arduino platform. F2F activities, based on a peer-assisted learning strategy, were complemented with tutorials and more advanced project suggestions in a blog. Pre and post surveys on students' attitudes towards programming and peer-coaching were administered to pre-university and first year college participants, finding an overall increase in the Likert scale for all the programming-related constructs under study (confidence, interest, gender, usefulness and professional) after the introductory course. As regards the peer-based learning approach, younger students seemed to be more eager to be taught in a less formal way than their older counterparts. The course resulted in high degrees of satisfaction for both the student tutors and their tutees. •Student-led introductory programming course for high-school students using Arduino.•Project-based approach for acquisition of computational thinking skills via PAL.•Pre and post surveys showed overall increase for all programming-related constructs.•Students totally agreed that women are as capable as men to excel in programming.•Significant age- and gender-related differences in attitude towards PAL were found.