This is nonsense. From my experience, as a union member, a building-level union counselor and, later, an administrator, neither statute nor accurate practice supports this misapprehension.
About all that tenure assures is the teacher’s right to a process of review established to justify, if necessary, his or her dismissal. Tenure is the fair alternative to being dismissed merely because of administrative dislike or political expedience. It is not tenure that prevents bad teachers from dismissal; but, "politics."
I have participated in getting teachers dismissed. It is, in fact, extremely difficult to remove teachers from their positions, no matter how abominably they perform in the classroom, if they have friends or relatives in high places. Nor is it likely they will be touched if there is a teacher shortage. Law requires, not a competent teacher, but a licensed adult to “cover” a class. Licenses are cheaply obtained.
Administrators are busy people, almost always “putting out fires” in their school community. It is really too much to expect them to be able to fairly and consistently evaluate the teachers – often many teachers – in their school.
And then there is the third issue: careerism. Administrators make substantially more money than teachers, in general, and, at retirement, receive substantially higher pensions. In Pennsylvania, a superintendent who averages $150,00 a year (a low salary) in any three years of his or her career and has put in 30 years service in any capacity in a public school system, receives a base monthly pension of approximately $90,000/yr for life. (Variations may occur depending if transfers to other funds outside the state pension system are made at the time of settlement.)**
A classroom teacher whose highest three years of salary during 30 years of service average $65,000 will receive a base pension of $39,000 – less if withdrawals are made. The point? Teachers who “rock the boat” threaten not only an administrator’s possibility of promotion; but, also their retirement income.
Principals get promotions if they don’t rock the superintendent’s or other local politicians’ “boats,” or if they step on those teachers who might rock the boat for them. Promotion in public education administration is substantially political, rather than based on clear, widely accepted technical criteria.
So it is that teacher tenure impedes the expedient, not-to-be-reviewed dismissal of whistleblowers, or of academically demanding teachers, or of targets of some vehement though likely evanescent community unhappiness.
The fourth issue is cowardice. Some people want to be leaders and bask in the deference accorded them by their subordinates. But they cannot discipline their troops when needed. So the most glaring incompetence will be tolerated, especially if it is accompanied by obsequiousness.
To examine these issues further, see Teacher Evaluation: Educational Process for Pedagogical Improvement Or Punitive, Political Tool?
** The general formula is this: Base pension per year = 2% x (years of service) x (average of three highest yearly salaries). For example, 2% of 30years = 0.60 If superintendent's three highest paid years whenever they occurred were $130M, $150M, and $170M, averaging $150M, then 0.60 x $150M = $90 before transfers, deductions and adjustments. Many retire with both 40 years service and higher salary averages.