Both teachers and doctors deal with a lot of variables they can't control. For teachers, students come in with personalities, drives, parents, learning history, strengths, weaknesses, home environment, cognitive differences, emotional differences etc. For doctors, there is pre-existing health, willingness to take medication, change lifestyle or other direction to alleviate symptoms, stage of illness, masking of symptoms by other issues, relative level of awareness by patients, differing levels of discomfort tolerance, different level of self-reporting, time of diagnosis, time to treatment (e.g. surgery schedules, MRI or other diagnostic scans).
In both cases, there is a clear recognition that the professional can't always fix the problem, and in both cases, there is a recognition that each can do something (teachers can take steps to move a student forward, even if they don't have the resources to "catch them up", doctors can alleviate pain in terminal cases, even if they can't provide a cure).
Why, then, the difference with respect to policing of their peers? Doctors accept that "things happen" and "patients die", but are willing to accept the judgement of their peers to help determine whether or not there was missed opportunities to aid the patient. This acceptance leads directly to some portion of doctors to be removed from the field should their performance not be considered appropriate by their peers - a recognition that while some negative outcomes are unavoidable, others could have had a less severe outcome if proper decisions and procedures were applied.
Teachers, not so much. Teachers, who are required in their jobs to evaluate and judge performance of students, tend to completely ignore or degrade the whole paradigm of assessment when it comes to their own performance, or the performance of peers. Talking one-on-one to teachers, they all can identify anonymous (or non-anonymous, depending upon who's asking) peers who are excellent, or deficient. However, any program that attempts to provide evaluative information is universally rejected by individual teachers and their professional associations. Why?
I believe part of the answer comes from the generic level of respect that the professions generate - doctors tend to be respected, teachers complain that their profession is under-appreciated. As most of the public had attended school, they all have a feeling that they understand teaching, and to a small degree, they do. However, the actual job of teaching has a lot more nuances and requirements than a student or parent can immediately see. As such, professional teaching organizations tend to have hair-trigger responses to any activities which might be seen as judgemental to individuals, and they adopt a "all teachers are equal" or at least an "all teachers are competent" model.
Doctors see patients relatively briefly, but over many years, typically one-on-one. Teachers see students intensely, but over a short elapsed duration, but in large class groups. Thus, the relationships between patients and doctors differs from that of teachers and students. Doctors must attempt to reconstruct the history of the patient from small windows, and make diagnoses in the windows allocated to that patient. Teachers have more complex relationships - they have to deal with personalities much moreso than doctors, because they are meeting daily for a school year, and they have to deal with many individuals with differing requirements simultaneously and repeatedly.
- time with patient/student
- scientific method application
- perception of external judgment
- perceivied use of data