Can we accurately evaluate the quality of a teacher?

I believe that teachers make a difference for students. I believe that an effective teacher can have a tremendously positive impact on student achievement in general and the achievement of individual students in particular.

Part of this is born from my own experience. I can reflect on the teachers that I had in my life and, anecdotally at least, identify the teachers who made a difference.

Part of this conviction that teachers make a difference is born out of the research. John Hattie in his book Visible Learning gives a nuanced and credible explanation of the potential contributions that teachers can have on student learning and achievement.

Having said that I am also aware that a student is only in a classroom for approximately 1098 hours a year. That is not a lot of time over the course of a year.

On any given day - in the approximately 180 days of a school calendar - a student may be in a classroom and in front of  teachers for approximately seven of their twenty-four hour day.

Yet even in the course of that day a student is in front of multiple teachers. At the elementary level a student in the course of one day may see their homeroom teacher and a PE, music, art, or media specialist during the day. At the middle and high school a student may see five to seven teachers during the course of their seven hour school day.

In addition, a student's day is cut up with lunch, recess, passing time, and the like.

Additionally, some, but not all, students have access to additional resources outside of school. The most important of those additional resources is a stable, compassionate, and loving home that encourages creative thinking, values independence, and is language rich. Those resources may also include trips to libraries and museums, access to computers, access to magazines and newspapers, and meaningful conversations with  interested adults. Clearly, access to those and other additional resources will influence how much and how easily a student learns.

So how can I determine the value added by a teacher to a classroom of students and to an individual student when a teacher's interaction is limited to no more than seven hours a day for 180 school days?

Yet I am responsible for evaluating teachers. I feel a great deal of responsibility to create a system that is fair and just to teachers. I also feel a great deal of responsibility to create a system that is fair to the students, and also to their parents, to ensure that the time students' spend in school is not wasted.

The question is how do I create a system that accurately evaluates the impact a teacher while recognizing the complexity of the task?