Diagnostic assessment is important to consider in the success of differentiated learning. Only 18.5% of teachers at Widiatmika Junior
High School prepare and compile diagnostic assessments as a basis for selecting differentiated learning strategies. Therefore, training on the use of artificial intelligence (AI) through ChatGPT was held to improve the ability of teachers to prepare diagnostic assessments at Widiatmika Junior High School. The training was conducted through a workshop consisting of theoretical and practical sessions. The results of the training showed an increase in teachers' understanding and skills in designing diagnostic assessments. Teachers' enthusiasm and active participation were seen in the practical session, where they were able to ask in-depth questions about the application of ChatGPT. This training successfully demonstrated the potential of AI in supporting the learning process. By using ChatGPT, teachers can develop assessments that are more effective and appropriate to the needs of students, thus improving the quality of education at Widiatmika Junior High School.