I wasn't a STA-21 guy, but I applied (and was accepted) for OCS as a junior schoolhouse Petty Officer with no Fleet time. I did one internal board with my chain of command, and an external with the designator I wanted (aviation).
The questions I was asked in both boards was very much in tune with STA-21.
1) Tell us about yourself (this was the intro, they wanted to get a feel of me).
2) Scenario: "You are an Ensign, and you see a Second Class drunk; it's the morning before muster. He just turned 21 last night, he's your best sailor in your division, and that day you are doing workups and you need him. What do you do." Another was how, as an aviator, you will lead a division of sailors as a collateral duty when you are busy flying. They wanted to see both reply to coordinate with the Chief.
3) What do you think about the phrase, "Mission First, Sailors Always"?
4) What is the new CNO doing that the old CNO did not.
5) What do you think about IAs?
6) What do you think is the Navy's Global War on Terror.
They also tried to rip me apart and explain myself. I was asked about my evals which were only standard Promotable, my medical drop from BUD/S Training and what I have learned from that experience, and one "What makes you think you will get picked for OCS, when you are up against all of these Fleet veterans who have earned their degree in the service and have glowing evals and endorsements?"