Having students “buy in” to the idea of composing their own music is very important at the beginning. Most students are very motivated to compose. When a student is not however, it is often because she may having feelings uncertainty or fear of failure.
Do everything to make it seem as though composing is a special thing that takes effort but also that it is something that everyone can do. Project for the entire class concert videos of other student’s work (Visit the Composition section of yciw.net). Explain how even if they have very limited experience with music they can begin to compose. Through composing music they’ll learn how it works!