I know these twins who were born about ten minutes apart, but one was born five minutes before midnight on August 31st, the other five minutes after midnight on September 1st. Here in England the age cut-off point is September 1st, so the twins had to be in entirely different grades!
Also, one of the girls I know from church was born on August the 31st late at night, and my mum asked hers, jokily, why she didn't hold on for a few minutes so her daughter would be the oldest in her grade.
The girl's mother said, very nicely, that her daughter was adopted.
Awkward!
Really awkward!
And the story about the twins just goes to show that any nonsense is possible, in life and fiction.