The Militia IS THE PEOPLE. In order to form a militia, THE PEOPLE must be able KEEP arms at all times to be able to effectively BEAR arms.
What is so hard to understand about this?
To accentuate the militia as being ALL the people who consider themselves to be US citizens, it should be a mandatory course of instruction at the high school level or even before, to first, familiarize ALL youth with the concepts of identifying firearms, the proper methods of their operation, the care, feeding and grooming of the devices with hands-on experience, and the rudiments of range training.
Determining legitimate targets, framing the target, and the capability to hold, aim and fire the weapons with a reasonable degree of accuracy, which means a LOT of range practice, should be a secondary part of the course (which would be spread over several years). In this span of time, those who are habitually careless, or who harbor malice toward others, would be identified, and steps may be undertaken to assure that they do not come into possession of firearms at any time. For those who are perpetually timid, and cannot be moved to take up arms under any circumstances, a further branch of this line of study may include the capability to avoid, evade, escape from, or even take on direct confrontation with an active shooter with malice intent, distracting his attention or even managing to neutralize him by unorthodox means.
That would have a number of advantages over time. There would be a vastly larger pool of potential military recruits or law enforcement officers, and the other young troublemakers will have considerably less scope to apply their bully ways.
The “greatest generation” who went away to fight the Second World War had much of this personal background already as they were growing up, when the culture of the arts of marksmanship and tactics were honed and impressed on a much larger part of the population.