My daughter now uses a pump but up until the beginning of Jan this year she was on the basal/bolus injections. She injected before meals unless we were unsure how much she was going to eat, for example trying a new meal that she might not like. Once we knew how much she was going to eat then we'd inject as soon after that as possible. Sometimes it meant injecting twice, for example out at a restaurant we'd inject for the main meal as we were unsure if she'd have dessert or what she'd be having for dessert. If she had dessert after the meal then she'd take another injection to cover the dessert.
It might seem a lot to take in now because it's going to be a new regime for you but you'll soon get into the swing of things and feel more organised about it.
I found with lunches that she liked a similar thing each day in her packed lunch so sometimes the amount of insulin being injected each lunchtime was pretty much the same. But we had the flexibility of being able to inject more or less if we needed to on those days that she wanted something extra in her lunchbox.
If she was low before lunch then we'd treat it as a hypo (glucose sweet) and then proceed onto lunch as normal with the same injection as she would have had with lunch even if she wasn't hypo. The glucose remedies the hypo so lunch follows as usual after that. If you find your son is going hypo frequently at the same time of day then either his basal or bolus ratio needs to be checked as it may not be right.
It took a little time with testing and experimenting but we also soon learnt how much her blood glucose would drop with different types of sport and different times of day and how long since the last injection. We found if she did sport within 2 hours of a bolus injection then her readings would drop more quickly than if the sport with 3 or longer hours after the bolus injection. In the beginning it's kind of trial and error but if you keep a log of injection times, sport type and BG readings you'll soon get a feel for things. It does make life easier if the sport is routinely at the same time of day each week. Our consultant did say that for sport rather than eating before the event we could reduce the insulin taken at the previous meal time, but we never did that because we found Jess wanted a snack before sport anyway (usually after school) so the snack worked well for us. Just to be clear, the biscuit was eaten without any injection done to cover the carbs, the exercise would burn off the carbs from the biscuit. If she wanted a snack after school and wasn't doing exercise then she'd have an injection to cover the snack.
Everyone is different but with my daughter we found a plain digestive biscuit before sport was sufficient to get her through without any hypos. She did half hour swimming lesson and 45 mins tennis lesson (not at the same time, two different days of the week). It all depends on the type of sport and the duration too so you may find some sports need more carbs on board than others.
For school make sure your son has access to a carb snack for sports. We found general PE didn't cause too much problem but they did cross country for a while at school last year and that really dropped her readings so she needed to snack on a biscuit before they started the session. It's a good idea to test BG before exercise and if it's an active session or a long session to test during the exercise too.
The book I'd recommend is "Type 1 Diabetes in Children, Adolescents and Young Adults: How to Become an Expert on Your Own Diabetes", it's around £20 at Amazon but well worthwhile. It's the book that really helped me a lot when we switched from the two injections a day to basal bolus. I know the consultants are there to help but the information you can learn in a book is so much more than what they can try and tell you in a 10 minute appointment once every few months.
Sorry for the long essay, it looks like a got a bit carried away!
