Shining,
When I think of mistakes, there are "positive and negative" versions of this definition. In the positive sense, trying new things or finding too little (or too much) time allocated for a segment of instruction could be cited as a mistake that a teacher learns from. On the negative side, making an intentional poor judgement or demonstrating unprofessional behavior would be examples of preventable mistakes, and should be avoided. I think a good rule of thumb is sticking close to the course objectives and planning the daily lessons (along with needed resources) carefully in order to assure the students… >>>