Observation/Evaluation - Observation for the purpose of evaluating the unit member's performance may be made at any time during the school year provided, however, that as a matter of general practice, the teaching performance of a unit member shall not be formally observed for the purpose of evaluation during the first day of school for students, the day before Thanksgiving, the day before the beginning of the winter holidays, the day after the winter holidays, the day before the beginning of the spring holiday, and the last day of school for students.