You have seen it a thousand times. Students come and they go. Sometimes they train hard and consistent, other times their attendance for whatever reason is lacking. There is no better way to help student retention than a personalized note sent snail mail.
Just purchase a few of these We Miss You cards, fill them out, write a personalized note to the student, add their address, put a stamp on them and drop them in the mail.
People get really motivated when they know you care about them and what better way to communicate that than with a handwritten message. It really motivates students to get back to class. Try them out now and engage with students who have been missing for a bit.