There is a simple answer.... schools stop the costly excess testing. If we were made aware of the cost of the exam development, exams themselves and grading/analysis - we would protest and rightly so. It is ridiculous to put the cost of supplies on the parents or the teachers - a basic necessity of teaching.
Ok, I'm getting off the soapbox. Ok, wait, one more thing. What would happen if parents refused to send in more than what their child would use? They can't kick the children out.