In this paper, it is set forth an action research case study, rooted in the principles of Multicultural Education and Teacher Education for Cultural Diversity and Inclusion. The study was developed in a Portuguese Public Secondary School with a cultural and social diverse school population, namely, immigrant students and those of the 2nd and 3rd generations of immigrant families from Portuguese-speaking African countries. The research was focused on a process of inservice teachers training and aimed teachers’ professional development for cultural diversity and inclusion. The research data analysis (interviews, field notes, teachers’ portfolios and reports of critical reflection) emphasised new conceptions on multicultural and inclusive education, changes in pedagogical practices, teachers’ reflexivity, students’ attitudes and behaviours, and school organisation. 2016 Annual Meeting of the American Educational Research Association, April 8-12, Washington Unidade de Investigação e Desenvolvimento em Educação e Formação da Universidade de Lisboa.