Since I've just started up a new studio, most of my campers will be beginners who've had only a year of piano. Some of them are more comfortable with notes on the staff than others. For the ones who are less so, I found a great idea in an article by Wynn-Ann Rossi, Original Composition: Dispelling Myths. She suggests using regular, lined notebook paper turned sideways with a line drawn across the middle of the page to represent middle C. Notes in higher octaves are written at the top of the paper and notes in lower octaves are written at the bottom. Notes that should sound together are lined up in the same column. I think this is a good solution for students who are either pre-readers or beginning notation readers. The number one goal is to get them creating, not to be stressed out over the details of writing it down. The picture represents my daughter's last improvisation - she loves open 5ths!
I like this quote from the article: "Counter to the myths, original composition is not a journey limited to young Mozarts. All children are creative. They deserve the opportunity to finger-paint their way into their own priceless musical identities."