We use the 30 a sheet computer nametags, print them out each week, we have ones pre-made on the computer at the beginning of the year with the kids names, grades, rotation. There are also blanks for visitors.
After class if over the teacher puts the sheet back on my desk so I can count attendance/see who wasn't there, etc. and I enter it all into Excel to we know what our attendence count is. That way our teachers don't waste precious teaching time with attendance (kids just get their own stickers), teachers can call them by name, and I can impress the session each month with a snazzy Excel document with our nursery-youth group attendance and show where our dips and gains are.
We get neon labels (not the boring white ones) from Quill to snazz it up for the kids. They like this and even wear them on their foreheads for the "cool factor", they like it and we keep track in a simple, quick, and efficient way.