Joe is right, you did contradict yourself. You originally said that tenure allows teachers to violate stupid school board decisions and to teach evolution anyway. Here, you said that tenure does not allow teachers to not teach evolution if the school board mandates it.
Which is it? Can the school board fire teachers for not following the curriculum? If so, then school boards can stop teachers from teaching evolution. If not, then teachers can choose to teach Creationism. Either way, tenure doesn't matter.
Tenure doesn't give them immunity to the school board and/or other administrators.
It does last long enough that abuses of the system and/or unofficial pressure to be resolved before the teacher actually loses their job.
Firing a teacher with tenure can take 12+ months.
Clearer?