Have you got Music Express in your school? If so, there's a lovely song in one of the Y6 units called Silver & Gold. The lyrics are about moving on and old friends and new, your new friends being silver and the old ones gold. Helpfully, for musical doofuses (eg. me!), the unit shows you how to split the song, with children split into two groupssinging different parts at different pitches (it sorts your tenors from your sopranos too). The music comes with it too. It's very effective.