A foundational finding I’ve relied on for nearly 20 years just got more complicated – and I want to make sure what I’m teaching reflects it.
For nearly two decades, I’ve been explaining the ADHD brain to parents, educators, and clinicians with a framework that felt solid. It was grounded in research. It made sense of behaviors that otherwise looked like laziness, defiance, or not caring. And it helped people extend grace to kids who desperately needed it.
Part of that framework came from a landmark 2007 study out of the National Institutes of Mental Health – work that Russell Barkley and others drew on extensively. The finding: the brains of children with ADHD mature more slowly, roughly 30%, or about 2 to 3 years behind their peers. It became foundational. I taught it. Most people in this field taught it.
New research has changed part of that picture, and I think it’s important to share with you all.
What the New Research Found
Published in May 2026 in the Proceedings of the National Academy of Sciences, this study used data from over 11,000 children and 26,000 brain scans – one of the largest neuroimaging studies of its kind. Researchers set out to replicate the original finding.
At first, they did. The same pattern appeared.
But then they looked more carefully. They accounted for something the earlier studies hadn’t: the fact that boys’ and girls’ brains naturally develop at different rates. Boys’ cortexes thin more slowly than girls’ as a matter of typical development. Since boys are diagnosed with ADHD at much higher rates, the earlier dataset had quietly skewed toward reflecting boys’ typical development – and researchers had been reading that as an ADHD-specific delay.
When they corrected for sex differences over time, the delayed maturation signal disappeared.
The conclusion: what looked like a hallmark of the ADHD brain was likely a mirage in the data.
What This Does – and Doesn’t – Change
I want to be clear about something, because this is where it matters for the parents, educators, and clinicians I work with.
This finding is specifically about one type of brain measurement: cortical thickness on an MRI. It challenges the structural, neuroimaging evidence for delayed maturation. It does not overturn what we know about how ADHD affects executive function – the skills children rely on every day to manage themselves, their attention, their emotions, and their behavior.
That evidence comes from entirely different research – cognitive testing, behavioral data, functional brain studies, and neurotransmitter research. And it is well-supported.
What we still know to be true:
- The prefrontal cortex – the brain’s manager for planning, self-control, and attention – works differently in kids with ADHD. It is less efficient at regulating behavior, attention, emotions, and follow-through than peers without ADHD.
- The loading and releasing of key neurotransmitters – dopamine, norepinephrine, and serotonin – is less consistent. This directly affects focus, alertness, and the ability to sustain effort.
• There is under-stimulation in the parts of the brain responsible for reward and motivation, which is why kids with ADHD often need more novelty, urgency, or interest to engage.
• None of this has anything to do with intelligence. It has everything to do with how the brain is wired.
The specific claim that needs updating is the “30%, 2-3 years behind” figure – particularly when it’s framed as a structural brain finding. The evidence for that precise claim is now on shakier ground. The broader truth – that executive function develops on a different timeline in kids with ADHD, and that this gap is real and significant – still stands. We just need to hold the specific numbers more loosely.
Why This Matters Beyond the Science
Here’s what I keep coming back to: the reason that the “years behind” framework resonated so deeply wasn’t the neuroscience. It was what it permitted people to do.
It gave parents permission to stop expecting a 10-year-old with ADHD to regulate like a 10-year-old without it. It gave teachers a way to understand why a student who seemed capable kept falling short. It shifted the story from “this child isn’t trying” to “this child’s brain is working differently.”
That shift still matters. The science supporting it is still real. What’s changed is one piece of the evidence – not the conclusion it pointed toward.
Understanding why a child struggles is never just an academic exercise. It changes how you respond in the moment. It changes whether you lean in with curiosity or frustration. It changes whether a child feels seen or blamed.
That’s what I’ve spent my career working toward – in how I train clinicians to coach parents, in how I work with schools, in how I support families directly. The knowledge isn’t the endpoint. It’s what we do with it.
What I’ll Be Doing Differently
I’m updating my teaching materials to reflect this. The “30%, 2-3 years behind” figure will come out. In its place: language that stays close to what we actually know – that executive function skills develop on a different timeline, that the gap is meaningful, and that our job is to meet kids where they are rather than where we expect them to be.
The research will keep evolving. It always does. My commitment is to stay current, to say so when something changes, and to make sure that what I’m teaching is as accurate as I can make it.
If you’ve heard me use the “years behind” framing before – in a workshop, a training, or something you read – this is the update. The heart of it hasn’t changed. The precision has.
What questions does this raise for you? And if you work with kids with ADHD – as a parent, educator, or clinician – what has the “developmental delay” framing meant in how you understand them?
I’m glad to learn this! It will change how I coach students and their parents. Thank you for sharing!💕