One form of teacher evaluation is based on looking at student growth. The evaluation of the teacher's performance as used in the the Tennessee Value-Added system looks at whether students are growing in their performance. Rather than focusing on meeting certain standards, both high performing and low performing students are measured in their growth. The teacher is evaluated on how their classes grow rather than whether they meet a particular standard. This approach is quite interesting in that it makes room for a more flexible view of student achievement and links teacher performance to that achievement. However, there are problems with this approach in that in some situations growth is maybe not possible due to situations beyond the control of the teacher (poverty, crime, violence, issues in the life of the students, or greater cultural issues). In my current school, growth would be very hard to achieve with many students due to a lack of motivation and a lack of overall academic interest. One could still be a strong teacher, who is organized, producing good lessons and is engaged with their students, but in one of these situations it might not be possible to achieve growth with the students. In such situations a teacher could be penalized for not achieving growth.
Another form is observation-based evaluations in which periodical observations form a basis for teacher evaluation and recommendations for development and improvement. In my personal experience with observations, I've found them to be helpful, but not necessarily an accurate encapsulation of me as a teacher. At my current school I've been evaluated twice in two years. This is odd considering that I teach in the high school, middle school, and elementary school. The method of observing teachers on such a limited basis is the rule rather than the exception in my career. While these observations have resulted in helpful feedback, it does not provide me with much opportunity for growth and development at the given rate.
I am interested in being evaluated on a more consistent basis with regular feedback to help direct my growth. The Teach Now rubric and system for evaluation seems like just this kind of system in that it provides detailed regular feedback aimed at helping me to grow as a professional. I think the level of detail of the rubric helps to fine tune a lot of details associated with teaching and to help the teachers in training to hone their skills.