There are two methods: 1) Make the subject matter more fun. This method only goes so far, but making the material come to life, relating it to the student's day to day life, and keeping it light are easy methods. 2) Give them some hope. When a student is struggling, they usually feel embarrassed or hopeless in the subject. The best path forward is to lob some easy questions at them and talk them through it in a way that makes them think that they came to the right answer before they have the full ability to on their own. Hope for future understanding is the best medicine for despair.