Start by letting students make up work at home if they miss days instead of making it mandatory that they attend a certain number of days. Give them the option of bonus schoolwork so that not every assignment is as critical to their grade if they miss a few. Have smaller class sizes so more attention can be given.
I remember getting bad grades and having to go to summer school once. We did very little schoolwork compared to a normal day and had a lot of fun. And somehow those few weeks made up for doing badly the whole year. Right now everyone's doing schoolwork from home, so what exactly about not being there a month or two is so important?