Q: Macbook snow leopard disk trouble

I work as a tech teacher at a school and we are trying to update all our old MacBooks to more current software. Mac OS X Snow leopard 10.6.3. from 10.5 For some reason the install disks we have keep getting spit out by the laptops after only spinning for a few seconds. Nothing is wrong with the disks since we used them very recently on other laptops in the school and they worked just fine. The install icon never appears and multiple types of restarts do not work to fix the problem, So what I'm asking is what am I doing wrong? Is there a way I can force the install into the laptop via the disk?