I have had a huge increase in retention when I began calling students immediately when they miss class. But, the other part is that once you reach them you have to stay positive about their chances of catching up once they return to class. I offer to email them missed information and assignments so that when they come back they will not be as far behind. Once students realized that I do care how they do in my classes and that I am here to help them be successful they now contact me before they miss class. I have also found that the number of overall absences drops, because I don't have students saying to themselves 'well I already missed two classes so what's another class going to hurt'. I ask them to treat class like their job; you cannot 'no call no show' for a job so they should not start the habit with class. They have really taken the concept to heart and generally my attendance rates have increased and the length of consecutively missed classes has decreased.