I have the members of my group numbered 1, 2, 3 and 4.

I assign sectionals:

Monday are the 1's
Tuesday are the 2's
Wednesday are the 3's
Thursday are the 4's

If a kid cannot make their designated sectional day, they can attend a different day that fits their schedule.

The above are not pure sectionals (as in only trumpets) but rather small group (25% of the band) practices with mixed instrumentation.