I was wondering a way for my student to have a practice cake so they can use every week, any suggestions, ideas?
There are many ways.....the cake pan; stacked up cake circles (wrap in press & seal plastic wrap); styrofoam; rice crispy treats......just a few ideas.
As a cake decorating instructor myself, I really encourage my students to always use a real cake to ice and decorate - particularly for beginners. Part of the decorating process is learning how to torte, fill, level, ice, and smooth a cake. Preparing the cake and being able to have a nice "canvas" to work on can sometimes be the most difficult part to master. Even if the class is focusing on something different each week, they still usually need the practice in preparing the cake.
That being said... if it's a time factor, or if it's for an advanced class that already has these skills then all the choices as listed above are great. JMHO