PurposeThe purpose of this study is to determine the effectiveness of an educational program implemented to support the sexual health and development of children with intellectual disabilities, using the Mastery Learning Model, on their knowledge of sexual health and development, as well as on their mothers' awareness of their children's sexual development. MethodThis study was conducted as a randomized controlled trial with 48 children who have intellectual disabilities, divided into two groups: an education group (n = 24) and a control group (n = 24). The program implemented was a sexual health and development education program based on the Mastery Learning Model. The data collection tools used were ‘The Sexual Development Characteristics of Children with Adolescent Intellectual Disability Scale’ for mothers and ‘The Sexual Development Knowledge Assessment Scale for Children with Intellectual Disabilities’ for children. ResultsFollowing the educational program, the children in the education group demonstrated an increase in knowledge regarding their sexual development and health. Additionally, the mothers in the education group showed an increased awareness of their children's sexual health and development. One month after implementing the education program, which utilized mastery learning, the children in the education group exhibited a greater level of knowledge compared to the control group. ConclusionThis study utilized the Mastery Learning Model to achieve effective and comprehensive sexual health and development education for children with intellectual disabilities. Practice implicationsPediatric and school nurses are recommended to use the Mastery Learning Model for sexual health education in clinics and school health practices.