Ideally, grade lesson plans should be orderly and sensible, but with enough room to include spontaneity and creativity. Anyone who has had to sit through a lesson plan that was rigid and tight, with absolutely no deviation from the tasks at hand, will know that this is a thoroughly unpleasant way to learn. Letting your students breathe a little is important in helping them learn and remember.
In some cases, grade plans must be scrutinized by a committee before the material is presented to students. This makes sure that the material and scheduling included is appropriate for the students as well as their overall grade level and abilities. Once the grade plans have been approved, the teacher is free to use them to the best of his or her ability.