I'm suprised by all the parents who volunteer that actually do real "teaching" during their volunteer time. Shelving books, making copies, etc - that all makes total sense. (And THANK YOU! to those who do it so the teachers and librarians can focus on other duties)
Chaperoning field trips, being a guest speaker, planning a party - again, that all makes sense and THANK YOU to those who do it so my kid can enjoy those events.
But I'd be a little annoyed if my kid's school used parents to do things like writing workshops and reading groups. That's the teacher's job. Sure, any adult can correct some spelling or grammar for a 2nd grader, but learning those things are the point of second grade and I expect the teacher to teach, guide, and monitor those skills. Not some mom who is (kindly) willing to spend some time babysitting my kid.

It sounds like the OP is jealous of a particular volunteer, and thinks that person is one upping their child.

I volunteer and am not sizing up anyone's kids. I think class sizes are too big and I help out so the teacher can focus on teaching and hopefully feel supported. I do what I am asked to do which has included:

-watch kids doing a writing assignment and help if needed while the teacher meets with reading groups

-sort papers

-read stories with small groups and ask questions

-set up for a class party

-chaperone a field trip

I enjoy children and I have yet to meet a child I didn't like. I have a special place in my heart for the kids who drive the teachers nuts because one of my kids is just like that. I am happy to have the spirited kids with me at a field trip or in a group.

Mostly they are busy-bodies who want to interfere in the classroom.