I was her proofreader all through her doctoral education, so pretty much through most of my high school career. This was before spellcheck, so I kept a dictionary at hand throughout. It was a way that I could help out and contribute. That and fixing supper and driving carpools and picking up groceries. The oldest child tends to get the most responsibilities. I don't think she ever had my younger sibs do any proofreading.
Anyway, I liked doing it. In my last job, I was the go-to girl for proofing and editing. In my current job, they don't believe in proofreading or editing (apparently). Sets my teeth on edge, it does.