Using Readability Formulas in the Classroom

There are three major methods of determining how readable (i.e. understandable) prose is.
1. The teacher, from experience, makes an estimate Teacher Estimates.
2. The pupil tries reading it (and a test can be used to find how well the pupil read) - Direct Assessment.
3. Someone applies a readability formula - Prediction Formulas.
However, each of these methods has specific uses - and specific limitations.