2nd class had to figure out a rule to decide whether a number was even or odd.  After a few weeks, they came up with a good definition! So here it is:

To see if a number is odd or even, you look at the last digit.  You look at the number line in your head and you see if that digit is a 0, 2, 4, 6 or 8.  If it ends in one of those numbers, the number is even.  If it doesn’t, it’s odd.

I couldn’t have put it better myself!