So what makes teaching (without research) so different?
In principle, tenure protects researchers whose results or studies are unpopular or not aligned with current political orthodoxy. So, say a conservative researcher works at a liberal school (or vice versa) and publishes something the administration doesn't like. Tenure protects him: they can't fire him because they don't like his ideas.
Tenure doesn't protect people who act fraudulently: that same researcher has to have proof to back up his claims.
The assumption behind tenure is that we expect that unpopular-but-true results will happen. As a society, we recognize that squelching research projects because some people just don't like them is counterproductive.
This situation doesn't apply (or applies very rarely) to primary and secondary school teachers. Even if it does apply, they aren't employed to do research: they're employed to teach a curriculum approved by a school board or other body. If they want to teach
and do research, they should go to a tertiary-level institution.
Sure, tenure may protect teachers from dimwitted or clueless administrators. But by that logic, everyone else in the world should have tenure, too. So I don't see this argument as a valid justification for granting tenure to teachers. In fact, using this idea for granting tenure just trades one problem for another. Sure, tenure protects good teachers, but it also makes it impossible or nearly so to sack the bad ones. The good ones have an easier time getting a job somewhere else, and the bad ones stay. Why would a less-talented person leave a secure job? Too much protection creates a tendency to mediocrity.
