JT probably has better advice for you on this than I but I'll share what I can with you.
First, I wouldn't call it a kick back. I quote package prices and then say there is an option for $2.00 per package to go to the sponsoring organization as a fundraiser. If they choose that option they need to provide me an assistant. The assitant collects the money (which is written out to the sponsoring organization). They provide write down image numbers by each student's name and provide me a list of students and packages purchased. They write me 1 check for the total less $2.00/package.
This has a couple benefits to me. I don't take the hit for bounced checks, they do. I also quote prices includeing sales tax. If the organization is a public school or pta/pto related to that school the sale is exempt of sales tax (at least here it is). So I'm paying near the same amount but I'd rather see it go to the school.
As JT has stated, it's a low end business. My cheapest package is $11.00 for an 8x10 and my highest is $17.50 for basically 5 sheets (equivelant of 5 8x10's). This is on par with others in the area, it's not discounted. I only make like $.20 per sheet extra as the packages get bigger. On average I earn $6.50 to 7.00 per package purchased. That does add up but it's a lot of work.
My advice, start small. Try to find a school with less than 200 students. I couldn't do a school larger than that without a duplicate set of equipment and another photographer.
Millers lab has good pricing on school packages. You might want to look into them.