We do it the same way as Deeisenberg, and bring everyone and don't stack anything at invitationals. Before regionals, we have a test off and use that and invitational results to figure out the best team for regionals, though we still bring everyone else and if some one beats the A-Team, we usually move them up. Our state and national teams are the same.
We didn't use test offs in the past, but we needed a way to distinguish which of two partners was better, so we added it two seasons ago.
We haven't ever really kicked someone off the team, though we did once lose a team member the night before nationals.
Nationals 2010- Astronomy: 4, Physics Lab: 4, Picture This: 4, It's About Time: 10, Optics: 2
Nationals 2009- Picture This: 4, It's About Time: 8, Astronomy: 9
Nationals 2008- Picture This: 2, Boomilever: 14