Observed score = true score + error
Error in how we measure student work can come from many places. Discrepancy in almost all assessments, if not observed, can imply correlations that do not necessarily exist. Compare all scores and data available. We live with error in most sciences, education not excluded, including how both teachers and students are assessed.
Video of classroom instruction is one of the most powerful professional development tools we have available today. You will be the most critical evaluator of your own instruction through self-reflection. Marzano's teacher evaluation model allows teachers to use powerful feedback on specific instructional strategies during specific parts of a curriculum. To help someone's skills move from Developing (2) to Applying (3) on Marzano's teacher evaluation scale, adapting to successes and challenges of strategy effectiveness should be taking place.