Measuring impact is a way of thinking. Our role as teachers is to know our impact, to understand this impact, and to act on this knowing and understanding.
An effect size measures the impact a particular influence or strategy on learner achievement. It is a calculation that is relatively easy to undertake and helps compare different influences. Teachers and leaders need to regularly gain feedback about the impact they are having.
Effect sizes are used by teachers to measure growth and to determine whether their teaching is ensuring a years growth for a years learning.