Lack of knowledge of effective educational interventions for gifted children is a pressing problem in Belgian schools. Most preschool and primary school teachers enter the profession without any training in the best practices for gifted children. This results in many misconceptions about giftedness and gifted education and a diversity of well-intentioned but ineffective interventions in the classroom. In response to the request for help from many schools, the Belgian expertise center "Exentra" designed a professional training program for in-service teachers with the aim to increase teachers' understanding of the characteristics and needs of gifted pupils, and help teachers develop the necessary confidence and skills to effectively teach the gifted in regular, mixed-ability classes. This study shows that the Exentra training is effective in changing teachers' beliefs about gifted education and enhancing teachers' knowledge, abilities, and self-esteem to effectively modify the curriculum for the more capable pupils in the classroom.