Background <p>We investigated the effectiveness of individual-Early Start Denver Model (I-ESDM) and group-ESDM (G-ESDM) intervention in children with autism spectrum disorder (ASD) at varying ability levels.</p> Methods <p>A total of 404 children were divided into I-ESDM (<i>n</i> = 237) and G-ESDM (<i>n</i> = 167) groups, receiving 3-month of intervention. The I-ESDM group had a staff-to-child ratio of 1:1, while the G-ESDM group had a ratio of 2:6. Clinical symptoms, neurodevelopment, and parenting stress were evaluated both pre- and post-treatment.</p> Results <p>After 3 months, both interventions significantly improved clinical symptoms, neurodevelopment, and reduced parenting stress in children with ASD. In the language age group under 2 years, the I-ESDM subgroup showed greater improvements in clinical symptoms compared to the G-ESDM subgroup. In the ≥2-year language age group and the general quotient (GQ) ≥ 70 group, the G-ESDM subgroup demonstrated greater improvements in clinical symptoms and neurodevelopment compared to the I-ESDM subgroup.</p> Conclusion <p>Both I-ESDM and G-ESDM effectively improve clinical symptoms, neurodevelopment, and reduce parenting stress in children with ASD. I-ESDM was more effective for children with a language age &lt;2 years, while G-ESDM showed better outcomes for those with a language age ≥2 years or GQ ≥ 70.</p> Impact <p><UnorderedList Mark="Bullet"> <ItemContent> <p>After 3 months, both individual-Early Start Denver Model (I-ESDM) and group-ESDM (G-ESDM) significantly improved clinical symptoms, neurodevelopment, and reduced parenting stress in children with ASD.</p> </ItemContent> <ItemContent> <p>The I-ESDM subgroup showed greater improvements in clinical symptoms in children under 2 years of age.</p> </ItemContent> <ItemContent> <p>The G-ESDM subgroup demonstrated superior improvements in clinical symptoms and neurodevelopment in children aged ≥2 years or those with GQ ≥ 70.</p> </ItemContent> </UnorderedList></p>