The opposite of “high” is “low,” correct?
So when a parent says their child is “high-functioning,” they’re saying other children are “low-functioning.” Even if they don’t think that’s what they’re saying, that’s precisely what they’re saying.
But what even determines high-functioning vs. low? Having a savant-like skill? Verbal acuity? Passing as “normal”?
My sense is that it’s that last one, that the term “high-functioning” is used by parents who feel their kids are close to “normal.” Their kids can pass. Maybe it gives these parents some comfort to use that label. I guess so, since I see it used out of context all the time. For example, some parents sign their emails, “Parent to Billy, high-functioning autism.” Ugh.