The emergence of Generative Artificial Intelligence (GenAI) tools raises discussions about their potential impacts on educational contexts. Teachers’ professional development (TPD) is seen as a fundamental process for them to feel confident to integrate GenAI tools ethically and with pedagogical value in their teaching practices. In Portugal, studies have revealed that teachers still lack the competencies to do so. To approach this issue, an artificial intelligence (AI) literacy TPD course was designed, encompassing modules that tackle knowledge about AI, the ethical challenges of its classroom integration, strategies to use AI in particular scenarios, and the design and implementation of lesson plans. In the five-month training course, 18 STEM teachers (from 8th to 12th grade) participated. Data were collected through surveys before and after the TPD course, training session recordings, and a focus group to gauge the trainees’ perceptions about adopting GenAI tools in their teaching practices and to guide their students in the ethical use of these tools. At the end of the training, teachers reported being surprised by the diversity of existing tools and the number of students who used them regularly. When they considered their actual implementation in the classroom, they mentioned that this process was challenging and required adopting methodologies that are more centered on the student and in the interaction between students and teachers. Preparing students for a future in which we cannot predict how far technological evolution will take us has become more demanding for teachers with the emergence of GenAI-enabled tools. One of the biggest concerns is related to students’ intellectual, social, and emotional development. In the study, teachers reported that the training they received helped them integrate GenAI tools with confidence and pedagogical value.