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Early intervention refers to services and supports for children from birth to age 3 (and through 5 in many systems) who have or are at risk for developmental delays, grounded in the principle that the developing brain's plasticity makes early experience especially potent. In the US, the Individuals with Disabilities Education Act (IDEA) Part C mandates free, family-centered early intervention services for eligible infants and toddlers, delivered in natural environments via Individualized Family Service Plans (IFSPs). Evidence-based interventions include applied behavior analysis (ABA) for ASD, speech-language therapy, occupational therapy, and developmental approaches such as the Early Start Denver Model. Research consistently demonstrates that earlier intervention onset predicts better outcomes across domains, with diminishing returns as children age — reinforcing the value of universal screening and rapid response.
Trace a hypothetical child from screening through evaluation, eligibility determination, IFSP development, and service delivery to understand the full early intervention system. Evaluate the evidence base for specific interventions (ABA intensity, naturalistic developmental behavioral interventions) and their effect sizes across outcome domains.
The core logic of early intervention rests on a biological fact: the infant and toddler brain is exceptionally plastic. Synaptic density peaks in the first two years of life, far exceeding adult levels, and experience-dependent pruning shapes which connections survive. Interventions delivered during this window can redirect developmental trajectories in ways that are simply not possible later. This is not a claim that development is fixed after age 3 — it is a claim about diminishing returns: the same intervention delivered at 18 months produces larger and more durable gains than at 36 months, which produces larger gains than at 72 months. The science behind this is what motivated policymakers to embed early intervention rights into federal law.
In the United States, IDEA Part C is the statutory foundation for early intervention. It entitles children from birth to age 3 with developmental delays or established conditions — and, in many states, children at risk — to a free evaluation and, if eligible, to services at no cost to families. The key document is the IFSP (Individualized Family Service Plan), which differs from the school-age IEP in a critical way: it is family-centered rather than child-centered. Services are designed around the family's priorities and delivered in natural environments — the home, childcare, and community settings where the child spends time — rather than in clinic settings. This design reflects evidence that skills generalize better when learned in context.
The evidence base for specific interventions is uneven. ABA (Applied Behavior Analysis) has the strongest research base for autism spectrum disorder, particularly when delivered at high intensity (25+ hours/week) in early childhood. Naturalistic developmental behavioral interventions like the Early Start Denver Model integrate ABA principles with relationship-based developmental approaches, with growing evidence for toddlers with ASD. Speech-language therapy, occupational therapy, and physical therapy are prescribed based on specific delays and delivered by credentialed specialists, often coaching parents to carry strategies across the day.
The key insight from your screening prerequisite is that the identification-to-service pipeline is where timing is lost. A child identified at a developmental screening visit at 18 months can begin services within weeks if the system functions well — but delays in evaluation, eligibility determination, or IFSP development erode the early-window advantage. This is why early intervention advocates emphasize not just the existence of services but the speed and quality of the pathway from first concern to first service.