And an editor reading this query would have a very clear idea of what you are proposing. There is no ambiguity about the story you're intending to write. You leaped over the highest hurdle of query writing, and that's great. And the other is to demonstrate that it is, in fact, a major problem nationally.
Statistics can help.
Ideally, you should be able to lead with a real child with a real reading disorder. Interviews with the child's parents and teachers would be terrific. The point is that you want to bring this story home to your readers. Many of them have kids and they'll identify with real people struggling with real problems. Finding a family might be difficult, and convincing them to talk to you certainly would be an uncomfortable task.