Hopefully you will receive hundreds of used laptops for your project. Erasing and installing Ubuntu will however then mean a lot of time consuming work until you can give away the laptops again. Therefore we need to keep the steps involved reliable, and as fast as possible.
For one simple but important reason I would rather suggest you go for standard Ubuntu rather than for the somewhat less popular variants Lubuntu, Xubuntu, or Edubuntu: people in rural areas will somewhat more likely get help for the mainstream Ubuntu than for the other variants. Only if you have many very old machines that can't even run Unity2D you may consider one of the more lightweight distribution variants.
download the installation CD
make a bootable USB drive from that (installation is faster than from CD)
alternatively user Remastersys from a running and updated installation to clone to the other machines.
For each laptop:
Boot with this USB drive (you may need to adapt the BIOS for that)
Choose Try out Ubuntu on the welcome screen to start a live session
Wipe data on the drives with any of the following in a root terminal
dd if=/dev/zero of=/sdx # for low security or when disks were encrypted
dd if=/dev/urandom of=/sdx # for a more secure wiping
/sdx with the appropriate for the hard drive(s), take care to not wipe your USB drive. For other secure wiping tools see this question.
close the terminal and choose "Install Ubuntu" from the same live session
Remove the USB and reboot when done
Update the system (optionally you may also install proprietary graphics drivers now)
By going through the above step of a live session before installing we have the advantage to see that the laptops are healthy, and we can also verify their hardware is capablae of running Ubuntu.