Jot it down! Problem with the memory is that we think it serves us well, but actually, it doesn't...
Evernote is a good tool to keep all your ideas synced up, even if it's written on paper. Just take a snapshot of it, make sure you have more than decent handwriting (you are a teacher!), and it becomes searchable!
Okieeeee - gotta jot it down! And yes to Evernote! :D