I can recommend Air Cadets. My son got a lot out of them - the chance to go gliding, shooting, plus representing his Wing for rugby, and has formed some lifelong friends from it. Plus he learnt how to iron his shirt and press his trousers, and Mum's standards were not good enough (phew).
A friend's son does Sea Cadets which is sea/water based if they are interested/like water. It's more boat based so canoeing, etc. tying knots and water based activities. Also things like new friends and ironing skills.
DS1 not a natural joiner did join the Air Cadets he was telling me in the car the other day how it really boosted his confidence. It's a big commitment twice a week about 48 weeks a year but loads of opportunities.
It has been hugely beneficial for DS. Cadets 'get' teenagers. The discipline is excellent without being bullying. The cost is low and kit is supplied. DS is going to annual camp in a few weeks. A week away with full board and transport provided cost less that £60 including all activities.
In our town all 3 cadet organisations share the same building (using it on different days). This includes a shooting range and an armoury! They shoot regularly with a lot of emphasis on safety.
Interestingly many of the Cadet NCOs at my DS's detachment are girls! Obviously just better at bossing the boys around!
My ds has just started air cadets and loves it. My dd1 does ccf through school and she is really enjoying it too. Both of them get to do things that they wouldn't do easily anywhere else. I was an air cadet and I'm still friends with people I met then
I did CCF at boarding school and loved it. Was in the RAF section so got to fly lots of dinky planes, run around fields in the middle of the night covered in shoe polish fighting the army section, shoot lots of guns (even qualified for Bisley) and meet some jolly nice boys from all-boys public schools on annual camp () - some of whom I'm still in touch with 27 years later!