This school year, I decided I was fed up with flipping over the centers groups cards from AM to PM (and back again). So I made two sets of cards, with name lines. I laminated the cards, so I could use a vis a vis marker that wipes off easily, as students enroll and withdraw. Now, I just slide the white centers cards, in the direction the arrow is pointing. Centers are about 20 minutes each and they change weekly.
To help children REMEMBER their groups, I send home a sheet that lists their group names, so parents can practice with their kid.