Ask a 9 year old: "who tidies up XXX in your classroom?". You might get a response like: "Mrs. Thomas makes us do it". A 5 year old's reply will be more like: "Mrs. Thomas lets us help". And, every parent knows how a "helpful" young kid can slow down the easiest of tasks.
Ironically, kids are most motivated to help with things where they cannot really very much. I think, it is in the nature of learning. If they know they can do something, there's no sense of acheivement left. If they've been there and done that, they lose interest, Instead, kids want to try their hand at tasks where they can achieve something.
With familiar things, there are some thing that Z still likes to do, only because he does them rarely: like making his own grilled-cheese sandwiches. Every now and then, he will remember that he can do that himself, and will get enthusiastic about it.
Today, he's making dinner for the whole family. I'm going to take a picture a little later and add it here. Okay... added. sorry it has a big chomp, but the cook insisted on tasting it, and wasn't patient enough to wait for the snap to be taken.