airlines aren't going to care...except for the weight.
customs will be luck of the draw. you may get raked, in which case it's good to have receipts. if you do get raked, watch out for the duty book. agents can or don't consult and you may be better off or not lol.
with all the new weight restrictions the best bet is to actually try and pick up supplies in Ja. or donate the cash. you never know what a school's actual need might be.
once i brought a box full of notebooks, pencils, etc, and they had a closet full of that stuff already. what they needed was modeling clay and a stereo that could play tapes.
you may also consider linking up with an org that reaches beyond negril to disburse.
head over to travelers if you have some time and buy some blocks.