HMH Explained Dyslexia’s New Definition. It Skipped the Part About Causes.

What did HMH’s pages leave out?

The International Dyslexia Association (IDA) wrote a new definition of dyslexia. Its board adopted it on October 22, 2025. It was the first change since 2002. Two new lines say what lies under the struggle:

“The causes of dyslexia are complex and involve combinations of genetic, neurobiological, and environmental influences that interact throughout development. Underlying difficulties with phonological and morphological processing are common but not universal, and early oral language weaknesses often foreshadow literacy challenges.”

HMH is a publisher. It makes lessons for schools. This month it posted a page of dyslexia resources. The page sums up the new definition in its own words:

“dyslexia is a specific learning disability characterized by difficulties in word reading and/or spelling that affect accuracy, speed, or both, and persist even when students receive effective instruction.”

It stops there. It stops before the line on causes. HMH’s October 1 post for the month stops at the same spot. That post links to a September 9 post by Tiffany Peltier. She is a director at HMH. Her title is “Why a New Definition of Dyslexia Matters.” She names the main change. It is dropping the old wording that was used to require an IQ gap. She also writes that sound trouble is common but “not universal.” She adds that reading trouble shows up in different ways. That is fair, and it fits the new definition. But the line on causes is still missing. We read her post on October 2. It never used the words genetic, neurobiological or environmental. So it never says genes, the brain and a child’s surroundings work together.

Other news did carry the line. NWEA posted a piece by Beth Praska on October 1. It quoted both new lines word for word.

Why does the line on causes matter?

For years, the common story about dyslexia was simple. It had one source: trouble with the sounds inside words. The 2025 definition moves away from that story. It calls the causes “complex.” It names genetic, brain-based and environmental influences. They work together as a child grows.

Sound trouble is still part of the picture. The IDA calls it “common but not universal.” So not every child who struggles to read has the same thing underneath. A plan built on one cause fits some children and misses others. Phonics is necessary. It was never sufficient.

To be fair, HMH knows the wider picture. In January 2025, HMH posted an article by Dr. Laurie Cutting. It lists several factors behind reading failure. It came out before the definition changed. The pages we read do not say dyslexia has one cause. Peltier’s post even says sound trouble is “not universal.” A parent who reads it learns that sounds are not the whole story. But none of the 2026 posts states the IDA’s line on causes. That line names genes, the brain and a child’s surroundings, working together. On causes, that silence leaves room for the old one-cause story. We keep a plain guide to the wider picture on our dyslexia page.

What should you ask about your child’s reading?

Keep the phonics teaching going. Nothing here is a reason to teach less of it. Every reader needs to sound out words.

Here is the tradeoff. A one-cause plan is simple to explain and quick to start. When sound trouble is the main issue, that plan fits. But a check that asks only about sounds will not surface trouble elsewhere. So ask the school two questions. What did you look at besides sounds? If this help stalls, what will you look at next?

Does your child need an IEP or 504 plan? Ask for a professional evaluation. Only that evaluation gets those supports. The same goes if you suspect a vision, hearing or medical cause. The definition changed in 2025. Let your questions change with it.