I was a Cadet, and then went on to do Junior Leaders just before I left.(www.juniorleaders.org) When I did the course it had a heavier emphasis on infantry skills and less ‘management training’ bollocks.
I was also lucky (?) enough to grow up and go to cadets near to the Commando Training Centre Royal Marines. (Lympstone) Many of my friends fathers are/were marines (and 1 para), and our cadet unit had strong links with the establishment, despite technically being crabs. (I don’t think we ever had any training support or rations etc. off the RAF, we just ran around on Woodbury Common doing the endurance course-slowly!) Several of my personal friends from school/cadets are now serving Royal Marines, as I decided to go to University before trying for a commission in the Corps, and they joined straight from school.
My military knowledge comes mainly from the (limited) training I recieved, voracious reading, especially of proffed PAMS and other countries military manuals, and constantly being around serving, aspirational, and ex. forces personnel as a teenager. I am also reading Strategic Studies at University, so I am fairly familiar with the more fundamental ideas about war and strategy etc. and with key texts such as Clausewitz and Sun Tzu.
EDITED TO ADD: I am also a very keen civilian shooter, and a bit of a gun/reloading geek, so I have gathered a fair amount of knowledge in this specific area.