If you plan on DONATING these laptops (being they are laptops) you should
format and install the original softwarer on it - as it came from the
factory. Then donate it. Such an act will be fairly destructive to the
data contained on the drive.
Same way you would on old desktop PCs...
Using some zero-write application is the best way to ensure it is HIGHLY
unlikely anyone would be able to get *your* data off the system.
A sledge-hammer and drill-press can all but guarantee it.