What this study is
The 1987 Lovaas study is the most cited piece of research in the history of autism intervention. Published by Dr. O. Ivar Lovaas at UCLA, it was the first study to demonstrate that intensive, early ABA therapy could produce dramatic, measurable improvements in autistic children — including outcomes that were previously considered impossible.
Nearly four decades later, it remains a foundational reference point — not because it was perfect, but because it was the first rigorous demonstration that early behavioral intervention could fundamentally alter the developmental trajectory of children with autism.
What the researchers did
Lovaas and his team worked with 59 young autistic children (under age 4) and divided them into three groups:
- Intensive treatment group (19 children): Received 40+ hours per week of one-on-one discrete trial training (DTT) for two or more years.
- Minimal treatment control group (19 children): Received fewer than 10 hours per week of the same type of therapy.
- Second control group (21 children): Received services from other community agencies — a real-world comparison condition.
The therapy was provided by trained therapists and parents, who were also taught to implement behavioral techniques at home. Treatment continued for a minimum of two years.
What the researchers found
The results were striking and, at the time, largely unprecedented:
- 47% of the intensive treatment group achieved "best outcome" status — defined as normal-range IQ scores and successful placement in regular education classes, with no autism-specific classroom support.
- The intensive group gained an average of 20 IQ points over the study period, compared to 8 points in the minimal treatment group.
- Language gains were substantially larger in the intensive group.
- Only 2% of the minimal treatment group reached "best outcome" status.
"The intensive treatment group children achieved significant increases in IQ and educational placement that were not achieved by the control group children." — Lovaas (1987)
Why this study matters
Before Lovaas (1987), the prevailing view in much of the clinical community was that autism was essentially immutable — that children diagnosed with autism had a fixed ceiling on their development. This study challenged that view directly.
It established three things that continue to shape autism intervention today:
- Intensity matters. 40 hours per week produced dramatically different outcomes than fewer than 10. The dose-response relationship between therapy intensity and outcome is now a well-established principle.
- Early intervention is critical. All participants were under 4 at the start. This helped establish the "early intervention window" as a major focus of autism research and policy.
- Parent involvement amplifies outcomes. Parents were trained as co-therapists, extending treatment into the home and across all waking hours.
Criticisms and limitations
The Lovaas study has been criticized on several methodological grounds, and it's important for parents to understand these limitations alongside the findings:
- No random assignment. Children were not randomly assigned to groups — assignment was based partly on therapist availability. This means the intensive group may have differed from controls in ways that affected outcomes.
- The "best outcome" definition is contested. Critics have noted that aiming to make autistic children indistinguishable from their neurotypical peers is a goal that many in the autistic community find ethically problematic.
- Replication has been mixed. Subsequent studies have generally confirmed that intensive early ABA produces significant gains, but few have replicated the specific finding that nearly half of children reach "best outcome" status.
- Early ABA methods were more rigid. The discrete trial training used by Lovaas in 1987 was more structured and repetitive than contemporary ABA, which incorporates much more naturalistic and child-led approaches.
What it means for parents today
The Lovaas study doesn't tell parents that 40 hours of therapy will produce any specific outcome for their child. Individual outcomes vary enormously. What it does tell us:
- Early, intensive intervention produces better outcomes than minimal intervention — this finding has been replicated many times since 1987.
- Parent involvement in implementing ABA principles extends the reach of intervention beyond clinic hours.
- The earlier intervention begins, the better the typical outcome — making early identification and early action critical.
For families who can't access 40 hours per week of professional ABA — which is most families — the research consistently supports parent-implemented ABA at home as a meaningful and effective component of a comprehensive plan.
Full citation
Lovaas, O. I. (1987). Behavioral treatment and normal educational and intellectual functioning in young autistic children. Journal of Consulting and Clinical Psychology, 55(1), 3–9. https://doi.org/10.1037/0022-006X.55.1.3