I guess I need to say this again. There is only one reason for “zero tolerance” policies.
INCOMPETENCE!
When a group of people that have responsibilities (real or implied) are in a position that could perceivable make decisions, they introduce liability. If there is concern that these “decision makers” are not competent, then they invite risk (litigation). The solution is to remove their responsibility to make decisions, thereby mitigating any liability. In this way, an institution can actually fire an employee (union contracts and all that) for violating the policy by “making a logical decision”.
It stands to reason, then, that our government teachers have been classified as incompetent to use good judgement and make good decisions by the very institution that employes them. But they are competent to regurgitate lessons from a book they follow.
And we wonder what is wrong with our public education system in America.
I believe you have nailed the chief reason. Nobody trusts the judgment of the person in charge at the lower levels. Constant policy revisions, forms and procedures are put in place to remove any room for common sense or judgment calls in dealing with students (or any one else for that matter)
I'm aware of one school system that wants its teachers to plan their lessons in 6 minute intervals instead of allowing them the freedom to adjust their teaching to the students' needs or shortcomings in a given area.
I have also seen it at the corporate level with manuals for offices even designating how many inches apart the desks should be separated.