The present article reports the results of a study performed to investigate and examine the characteristics of a teachers' professional development program (Teachers' Professional Development Program for Differentiated Instruction [PDD]) specially designed to support teachers in the design and application of differentiated instruction. Considering the characteristics of high-quality professional development programs (i.e. active learning, collective participation, closely related to the curriculum and the existing teaching realities, sufficient duration and continuance), the PDD aimed to facilitate change in both attitudes and practices of the participants. The study provides evidence of the success of the program, both in terms of teacher professional development and student achievement, and discusses the elements that made this program successful.