The DAFNE people say to use fruit juice. You can buy packs of 200ml cartons that are easy to keep all over the place: in the car, school bag, bedroom, kitchen and anywhere your lad frequents. It's worth keeping some somewhere in the school sports section.
Lucozade is awful to use because it is so fizzy, you can't get it down quickly and have to sip it while the hypo gets worse. At least, that's what I found when I used to use it.
I used to use cartons of Ribena too, but the DAFNE course people said there was too much glucose in each one, and fruit juices are better. Ribena works much quicker though, because it has glucose syrup in it which goes straight into the blood without needing any breaking down first.
Then eat something solid about ten minutes after the juice. I have always found that tablets, like the dextrose etc, are very difficult to dissolve because my mouth goes dry with the hypo and those tablets need a lot of saliva to get them down, and I don't know if it there is any science in this or not, but I have found that they don't seem to start working until you have a drink too, so you might as well use sweet liquid if you've got to drink anyway. The tablets are also fiddly and difficult to open and handle with shaky hypo hands and brain.
If there is nothing else available, two or three spoons of sugar in some warm water, stirred well and gulped, works as well as anything else. There is absolutely no point buying specially made, expensive things that say they are 'made for the job', when a few spoon of sugar, or 'value' orange juices from the supermarket, work just as well.
Good luck with it all.