All public schools of this state may observe such legal holidays as may be designated by the local school board, and no sessions of school shall be held on holidays so designated and observed. However, all schools shall operate for the full minimum term required by law exclusive of the holidays authorized by this section. The holidays thus observed shall not be deducted from the reports of the superintendents, principals and teachers, and such superintendents, principals and teachers shall be allowed pay for full time as though they had taught on those holidays. However, such holidays shall not be counted or included in any way in determining the average daily attendance of the school.