Early intervention is a service for preschoolers with cognitive, emotional, or physical disabilities that helps them improve their functioning and performance in regard to participating in school or everyday life. Purpose: To enhance the quality of internship education in clinical psychology, the objective of this study was to measure the effect of competency-based education (CBE) and competency-based assessment (CBA) in the early intervention of clinical psychology training programs. Methods: We provided early intervention for preschoolers with suspected autism spectrum/emotional problems, suspected developmental delay/cognitive problems, or suspected attention-defi cit/hyperactivity problems. We used Core Competencies of Rehabilitation Psychology (CCRP) to explore four domains of competence before and after the intervention, including: (1) psychopathology of rehabilitation psychology and neuropsychology, (2) case formulation, (3) skills of psychotherapy, and (4) psychotherapy process and procedure. Results: Trainees and clinical supervisor assessed significant improvements in the four domains of competencies among three types of preschoolers (p ＜ 0.001). Furthermore, feedback received from caregivers after the early intervention showed a high degree of satisfaction. Conclusions: The core competencies are the foundation required for high-quality mental healthcare. The experiences of CBE and CBA might help to improve the clinical psychology internship training program in Taiwan.