Here's a round that fun to do with your upper grades. It's great because it contains ti, which is a melodic element that I focus on in 5th grade. It's "eerie" without being Halloween based, so if you have students that don't celebrate Halloween this will work for you.
Here's the round:
I took four levels of Kodály at Portland State. But when I did my masters at Colorado State University (with a Kodály emphasis) not all of my credits transfered and I took levels II and III (again: with Sue Liethold-Bowcock and Ann Eisen). During choir at level II @ CSU Ginger Littleton used a choral arrangement of "Old Abram Brown" that was essentially the round, with ths coda (tag) at the end:
The kids love this round. AND it works great on concerts!