Differentiated Instruction (DI) is considered as the teaching approach that builds upon children's differences in order to address them and consequently lead each and every child to academic success. Although DI seems to be an effective teaching approach, teachers' perceptions and/or misconceptions, as well as unsuccessful attempts of implementation, constrain its inclusion in everyday practice. Therefore, the need for appropriate and effective Professional Development programs (PDp) is emerging in order to clearly define the concept of DI and facilitate the application of related practices. The aim of the current study is to shed light onto teachers' experiences with DI, through a PDp, which was developed to provide effective support to teachers to change their perceptions and teaching practices and apply successfully DI. The participants were 7 in-service kindergarten teachers. The program lasted 8 months and included deepening on theoretical and practical levels. Multiple tools were used for data collection, such as open-ended questionnaires, personal diary of the researcher and individual semi-structured interviews. Content Analysis showed that teachers initially had misconceptions about the concept of DI and doubts regarding its applicability, while during the program they realized its positive impact on children, which encouraged them to continue their differentiating practice. According to teachers, the successful elements of the program, which contributed to the revision of their personal theories and generally their professional development, were the cooperation with colleagues in a warm and welcoming climate during the meetings, the long-lasting duration and the constant feedback and reflection. To conclude, the PDps provide the necessary context for the teacher to experiment with DI, though the prediction of future application is not yet sufficiently studied.