Can you be barred for not going to a promotion board in your secondary window?

You can be barred for failure or lack of desire to progress. Also, his reason is nonsense. He can spend a couple minutes prepping for the board and it will certainly make his chances of being selected for the commissioning program he's applying for much better

When I was a young SPC, I was VERY good at what I did. I maintained a high personal and professional standard and I was an excellent peer mentor. But... I was not personally ready to lead Soldiers in an official capacity. I am STILL just a little bit bitter about being forced to go to the SGT Promotion board before I was ready and willing to take on that added level of responsibility.

So.... I completely understand where that Soldier is coming from. However, if that Soldier is working to become an Officer, that Soldier has identified a desire and willingness to lead Soldiers. If he is unwilling to prepare for a promotion board, which is designed to identify and showcase his leadership skills and potential, then he is honestly not ready to contemplate becoming an Officer.

We expect our Officers to have all of the leadership skills and knowledge that we expect our NCOs to have. And then some. And to do it under more stress, at a higher level, and in a greater capacity. If a Soldier is not ready for the SGT Board, they DEFINITELY are not ready for OCS.

Simple answer, yes.