Although this is all from memory, I'll bet a tidy sum I'm very close to
completely accurate on dates and so on.
Student deferements continued in effect until the institution of the lottery,
the first drawing for which was in early 1970 (possibly late 1969).
Therefore, those who had entered school as late as 1969 with a student
deferment were protected from the draft until normal graduation in 1973, by
which time all American troops were withdrawn. Those unfortunate enough to
have a low lottery number in 1970 could conceivably have come to the top of
the draft roles, been called up, trained and shipped off to Vietnam by
mid-1971; it's highly unlikely that anyone tagged by the lottery could have
gotten there sooner. Look at the casualty figures from mid-1971 onward.
The point here is that, although I don't know of any hard data, very few young
Americans identified through the new, "more just" lottery ever served in
Vietnam and a very small proportion of them were casualties. Despite the
impression that is given today that an unfair system was reformed, the student
deferement remained an effective way to legally avoid Viet Nam throughout the
war, and the burden was borne by those who couldn't--or didn't--avail
themselves of it.
Jim Lynch