It's too variable. A teacher has a variety of classes with a variety of children that changes completely every year. The outliers are enough to impact the metri

It's too variable. A teacher has a variety of classes with a variety of children that changes completely every year. The outliers are enough to impact the metrics significantly but leaving them out paints an unclear picture. As well you have additional high variability of an individual students performance at any given time. This variability is greatest in the non-outliers which matter the most.