There are many positive ways than to encourage any employees ( teachers ) to be honest about sick days.
One option, give the sick days as cash, retirement plan donations, or as vacation days at the end of the year if they are not used.
Having every Friday swamped with subs sends a terrible example to the students. The students are being cheated on their education.
Second option, if the students excell in state wide tests, then bonus time or money could be offered for positive results.
There are many other positive ideas, too.
That sounds good. If there was a "buy back" format of some kind where there was an incentive to accumulate unused days, there would be less temptation to "use them or lose them"
I know of a teacher nearby who took her family to DisneyWorld on the second week of January. Missed an entire week of school right after having been off two weeks for the Christmas break.
Insanity.