Many art classes are formed by age. The children segmented into different age groups and then fed the same curriculum assuming that they are at the same develpmental level and maturity. The teacher demostrates at the beginning of the class and everyone produces the same sort of work.
This way of teaching allows more of the children to produce the same "ideal" kind of artwork. Which piece of artwork looking like the next.
However, I never do that in my class. Why?
Take a look at the self portrait sculpture built by Sophia (5 years old)
Now let's contrast it with the self portrait sculpture built by Caley (7 years old)
Despite the age difference, we can clearly detect the maturity in the younger student and the difficulty the older student has in expressing 3D forms. He simply expressed it in terms of lines.
Why not just show them how to do it through demostration then? Right at the beginning of the class. Well, I can, but I will disrupt the creative process of the child. I end all thoughts and expression that originates from the child if I show them the "correct answer". By allowing this exploration, we allow the child to show us their solution and their expressions.
So a fine balance is maintained. To allow the child to first express and then discover and learn the next steps to progress.