K and 1 teachers at my school teach the kids to replace it with a capital if you can't remember what way the lowercase goes.
While this works great in k and 1 - it means that this year I am teaching kids how to write lowercase b's and d's!
I don't worry about it until we check for conventions. That's when I'll say "whoops! does that say do or bo?" I'll circle all the letters in pencil and send them back to correct it.
In k and 1 I would start by only correcting the letters on publishable work as well as handwriting, spelling, their name. As the year continues, hold them to a higher standard and begin to require it on more work. Perhaps on all of it by the end of the year?