The experimental group consists of 33 children diagnosed with early signs of neurodivergence or diagnosis of autism. The sample is aged between 18 and 48 months

The Early Start Denver Model (ESDM) is an early naturalistic and behavioural intervention for children with initial signs of neurodivergence or on the autism spectrum between the ages of 12-48 months. This early intervention aims to increase the rates of development in several domains and to decrease the characteristics of autism conditions that hinder children's ability to learn from everyday experiences and interactions.

The Autism Diagnostic Observation Schedule-Second Edition (ADOS-2) is the "gold standard" for the assessment of autism spectrum disorder. It is an activity-based assessment evaluating communication skills, social interaction and imaginative use of materials through five modules:

• Toddler Module: for children from 12 to 30 months who have not yet developed fluent language. It provides a risk indicator.
• Module 1: for children from 31 months without fluent language. Autism Spectrum: total score ≥ 12 Autism: total score ≥ 16
• Module 2: for children who produce complete sentences even if not fully fluent, even under 30 months.

Autism Spectrum: total score ≥ 8 Autism: total score ≥ 12

• Module 3: for children and young adolescents with fluent verbal language. Autism Spectrum: total score ≥ 7 Autism: total score ≥ 10
• Module 4: for late adolescents and adults with fluent verbal language. Autism Spectrum: total score ≥ 7 Autism: total score ≥ 10

The Griffith Mental Development Scales (GMDS-ER) assess the developmental quotient of infants and young children from birth to eight years in five developmental areas (Griffith, 2006):

• Locomotor (gross motor skills including balance, coordination and control movements);
• Personal Social (personal independence and social development);
• Hearing and Language (receptive and expressive languages);
• Eye and Hand Coordination (fine motor skills, manual dexterity and visual monitoring skills);
• Performance (visuospatial skills, speed of working and precision). Subscale quotients are calculated by dividing the developmental age corresponding to each subscale by the actual chronological age and multiplying by 100.The General Quotient (GQ) and each subscale quotient have a mean of 100 points (Standard Deviation (SD) = 15 points).The GQ raw score is the sum of the subscales raw scores. A GQ or a subscale quotient <70 points (>2SD below the mean) indicates developmental delay.