I also started my art teaching career middleschoolers in a charter school and
I found these two books very helpful: Hooked on Drawing by Sandy Brooke and A
Survival Guide for the Elementary/Middle School Art Teacher by Helen Hume. I
would also recommend subscriptions to School Arts and Arts and Activities
magazines. Last but not least, I found the websites of some of the teachers
on this list invaluable in developing lessons. Good Luck!