I appreciate your kiddo's art project... a very fun and thought-provoking piece! The perspective is excellent, highly complex, intricate, and detailed.
As for the teacher's complaint that your son worked ahead... Some may say that art is about more than following formulaic steps... it is about exploring, experimenting, developing one's "eye" and sense of style, proportion, symmetry, asymmetric balance... and as one develops their eye, adjusting & erasing are a normal part of the process... a positive sign of one's ability to critique their own work, to have an internal conversation which allows them to self-correct.
If erasure marks show, possibly your son might benefit from having a better eraser, such as artgum, rubber, or kneaded eraser, and possibly better paper as well. Whether in art or another endeavor, people may often find their growth limited by the materials at hand; They may experience great growth and also satisfaction with their efforts when the materials are upgraded. There a number of discount art supply stores online, including Dick Blick and Jerry's Art-a-rama.
IMO, art class is a place where there ought to be talking privileges, especially as students refine their work, and may seek casual feedback and share compliments. As art is an expressive skill, studio time may be thought of as an expressive time.
Please consider helping your son develop a "portfolio" of his works, including this piece.
Unfortunately, some teachers do retaliate with "designer grades", calculated to just miss a grade cutoff (
or conversely, design a grade to boost a student .01 above a cutoff). Old threads on the forum discuss the impact on grades from
selectively allowing do-overs, and also the seemingly somewhat arbitrary assignment of
grades on a scale of 1-4.
Given the circumstances, you may wish to consider whether there is an appeals process for grading.
