But mnemonics are great - we all know 'big elephants can always upset small elephants for 'because', right? So when I first started teaching, I made up a silly mnemonic (sillier ones are easier to remember, I think) for would/could/should. I teach it to my class every year, and I don't usually have problems with kiddos remembering how to spell these words (in our spelling assessment on Friday, only 1 child spelled 'would' wrong - and that child got 'could', funnily enough. Who knows what was going on there?).
So - for 'would', we remember 'Would otters upset lucky ducks?' To change it to 'could', we just remember 'Could otters upset lucky ducks?', and 'should' becomes, 'Sh...otters upset lucky ducks!'
Easy peasy! The kids really do remember it, just like they remember the elephant mnemonic for 'because'. If you try it and it works for your class, let me know!