The transition from secondary school to STEM higher education constitutes a critical stage that frequently exposes gaps in students’ foundational scientific competencies, including data interpretation, mathematical reasoning, measurement, modeling, and scientific communication. These difficulties significantly affect students’ academic trajectories and contribute to early dropout in science and technology degree programs. This paper presents an interdisciplinary educational intervention designed to support secondary school students during the transition to STEM higher education through a series of seven structured workshops complemented by technology-enhanced domiciliary activities. The intervention integrates core concepts from physics, chemistry, mathematics, and biology, emphasizing active learning, collaborative problem-solving, and the development of transversal scientific skills. A distinctive feature of the proposal is the guided and critical use of artificial intelligence tools in extracurricular activities carried out outside the classroom. Students are encouraged to compare their own problem-solving processes with AI-generated outputs, identify conceptual and methodological errors, and reflect on the epistemic limits, risks, and potential of AI in scientific learning. This approach promotes metacognitive awareness and responsible use of emerging technologies. Implemented within a university extension framework, the model fosters institutional articulation between secondary schools and higher education, supports inclusive access to STEM careers, and positions extension-based interventions as effective pedagogical strategies for strengthening STEM readiness prior to university entry.