The goal of education is to get students to think, learn skills and learn information. Unfortunately the only way we have to evaluate students is to test them with tests that we hope are uniform and standard. To start, we must recognize that any test score has a measure of experimental error, and educators frequently improperly analyze test scores. To the extent that tests are correctly written and properly administered, the tests evaluate the progress of each student both in learning information and skills and acquiring the ability to process this information. The tests do not evaluate the teacher.
The classroom teacher may be the most visible person in a school. They may be in direct contact with the student anywhere from 1 to 6 hours per day. They bear the primary responsibility of presenting lessons to the student and evaluating the student's progress on a day to day basis. Nevertheless, the classroom teacher is only one of many significant influences on the student.
Motivation is a significant factor in academic success and lack of motivation frequently aims a student toward failure. Teachers, coaches and principals work hard to motivate students, but their power is limited, especially in those cultures and communities where teachers are not given much respect. In my experience, parents have the most influence over motivation. Successful students usually have at least one family member encouraging their success. Unsuccessful students often have parents or other family members sending the message that "Algebra, English or some other subject isn't important." They may even send the message that school in general is not important.
Peer groups also motivate or demotivate students. More than ever before, pleasing one's peers is highly important to a student. When a student's peers do not think a certain class or teacher is cool, it becomes very difficult for students to become engaged in that class. For that matter, there are peer groups who advocate that school is not important. To them a GED is enough. Other peer groups are more interested in having fun than in learning.
Society itself does not encourage education the way it once did. While society gives lip service to getting a diploma or a degree, knowledge takes a second place. Parents of students who fail to meet graduation requirements frequently look for loopholes to help their student "walk the line." Students are told it is important to get a college education, yet admission standards are lowered so that almost anyone can get into college. At some community colleges the typical student spends up to two years taking remedial courses before they can start taking courses for college credit. This gradual erosion of admissions requirements and degree requirements cheapens the value of a degree and the students know this.
Class size strongly impacts academic success, yet the teacher has no influence.
Teachers have little input into textbooks or the types of supplies available.
The design and maintenance of facilities are out of the reach of teachers.
Scheduling of the school day and interruptions such as assemblies are not controlled by the teachers.
Those of us who teach, teach for the express purpose of improving the minds of our students. Would that our students would become sponges soaking up the skills and information we present. Alas, we recognize that we are each only one small piece of the overall picture. We make our contributions in a series of small accomplishments. At the same time the students are impacted by so many other variables. Perhaps the greatest variable is that while some students are eager to learn, others could care less. Even a poor teacher can be highly successful with the prior group. The best of teachers has difficulty making progress with those who do not care to learn.
There are ways to evaluate a teacher, but the test scores of students do not adequately quantify the role a teacher plays in education.