Your expectation of what the secret service should and should not do in a given situation is irrelevant.
You are talking about highly trained, highly dedicated individuals, whose profession is to protect the most important people on the planet. This is their job; this is what these people do, everyday.
You are in no position whatsoever to question the judgement calls these individuals made in that school, because you are not a highly trained professional.
The building was secure, the president was in not immediate danger so they had absolutely no reason to move him, manhandle him or advise he did anything.
The fact that Bush sat their like a stuffed dumby while the US was under attack is prove, if anything that he did not have a clue that what was going on, let alone have fore knowledge of it.