That boy in the school was not in any militia.
Actually this is not true. The militia is;
10 U.S. Code § 246 - Militia: composition and classes
(a)The militia of the
United States consists of all able-bodied males at least 17 years of age and, except as provided in
section 313 of title 32, under 45 years of age who are, or who have made a declaration of intention to become, citizens of the United States and of female citizens of the United States who are members of the National Guard.
(b)The classes of the militia are—
(1)
National Guard and the Naval Militia; and
(2)
the unorganized militia, which consists of the members of the militia who are not members of the
National Guard or the Naval Militia.
The fellow is part of the unorganized militia. In practice we regulate the dickens out of (1) and do little with (2).
In the past we have call them to duty, the last time it was called the draft, administered by your local Draft board.
I think young men still must register upon reaching the age of 18 although they do not get called as it stands now.
The use of the militia in the 2nd amendment in my view is one of the reasons for the right that shall not be infringed.
However, It is not the only reason. As at least Madison knew, we the people have the God given right to defend ourselves and our rights with the force of arms when necessary. This has been a long standing right recognized in Natural Law.