There is no better way to help student retention than a personalized note sent snail mail. Especially when it is a birthday card.
People love getting things in the mail. Show that you care about them by remembering to send them a card on their birthday.
Just purchase a few of these Birthday 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.