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?
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.
Another way to phrase that would be: Teachers can violate such a ban temporarily.
It isn't blanket immunity and that isn't what I said.