Question for British list members (school years)

[Carol]

Catlady wrote: 
> In my old mind, students were 5 in kindergarten, 6 in first grade, 7
in second grade, 8 in third grade (and were so impressively big and
grown-up when I was in kindergarten!}, 9 in fourth grade, 10 in fifth
grade, 11 in sixth grade, 12 in seventh grade, 13 in eighth grade, 14
in ninth grade, 15 in tenth grade, 16 in eleventh grade, 17 in twelfth
grade. By 'in', I mean they turned that age by a stated date in that
grade, such as September 30 or October 15 -- thank God/dess my mother
managed to start me in a school district where the cut-off date was
November 30!
> 
> This is clearly not the case nowadays, when news reports are always
full of 18 and 19 year old high school students who are old enough to
vote, enlist in the military, and sign contracts without parental
consent. Do you know when it changed, or is my memory just wrong?

Carol responds:

The ages didn't change, AFAIK, only the month when the children had to
turn five to be enrolled in kindergarten. When I was little, the
school districts used the calendar year, so a child had to turn five
by December 31. The oldest kids were those born in January; the
youngest, those born in December.

Now, AFAIK, they use the same school-year calendar as the WW: A child
has to turn five on or before August 31 to be enrolled in
kindergarten, so the oldest children are those born in September and
the youngest, those born in August. A child born in summer (June,
July, or August) will be the same age for the whole school year (just
as in the HP books).

As for nineteen-year-old high school students, I don't see how that
would happen unless a kid was held back a year or two, and in these
days of social promotion, I doubt that happens very frequently.

The system could, of course, differ from state to state. I can only
speak for Arizona. And I don't know exactly when the age requirement
changed, only that it's been that way at least since the late 1990s.

There will be Hermiones (the oldest kids in the year) and Harrys
(among the youngest in the year) regardless of the system. 

Carol, who graduated from high school at eighteen because of her April
birthday and would have done so regardless of the cut-off date