In my current school district, IEP (Individual Education Program) is assigned to students that need help, and parents are actively and explicitly ask for it, even if the kids are borderline. Please note that, this doesn't take away resource for regular kids, in fact, classrooms with IEP student get more teachers so everyone in that class benefits. IEP students are also assigned to regular classroom so they are not treated differently and their identities aren't top secret. Mind you, the parents here can easily afford additional help if needed.
In other neighborhood, a long time family friend with two young children, the older one doesn't talk in school, period. Their speech is clearly behind. The parents refuse to have the kids assign IEP and insist that as long as the child is not disruptive, there is no reason to do so. Why the parents don't want to get help, because they feel the older child will get labelled and bullied and treated differently. The older child hates school and they are only in kindergarten. Teachers don't know what to do with the child.
There is a limited amount of money in the school system. When resources are assigned to one place they are taken away from somewhere else. The kids in the class without IEP students are getting boned by this policy.