I've had my share of those types of classes...my first years teaching were in an urban setting (k-5) and I felt as though i was thrown into the lion's den! I remember using an incentive called best table(s). Each table earned stars during the class for mostly being on task. I would write them on the board. When they reached a certain number (usually 5), I would give them a reward (like feathers as the finishing touch to their Kachina doll , gold paint to add highlights to their mummy case, glitter to add to their maraca, etc) It worked and if I couldn't think of a special supply , there was always candy. :)
I'm in a semi-rural setting now (5th-6th) and use points per classroom. They can earn 5 points each class (entering quietly, silent during directions, quiet work time and on task, orderly and timely cleanup, and quiet lineup). I keep track on a chart and they earn priviledges for points - such as at 10 points they can use the sensor sink (yes this really works and 5th gr is so excited about this!) , 40 points they can use the ELECTRIC pencil sharpener (there is a manual one they use up to that point) , later points include... music in class, change seats for a day , art bingo and perfect score at end of year I buy them freeze pops and cheese curls and we call it a party!
My brother teaches art in Harrisburg, Pa and I know he calls home (ALOT).
He gives a reward day (video, snack) every 7th art class or so - if they earn it. Hopes this helps, hang in there, Beth in Dover, PA