What age group are you teaching, children, teens or adults?

What kind of clay will you be using, an oil-based clay like Plastacine, or a drying clay like terra cotta?

Are the portraits being hand-carved from the clay, or are you using plaster-bandage material directly on the human faces to form a sort of identical mask?

Plasticine clay is oil-based, so it shouldn't need any release agent. You can just start laying the paper on the clay surface.

If you're using water-based natural clay and letting it dry, you will need a release agent like an oil or petroleum jelly.

Some people like soft papers like newspaper, others like firmer types like brown paper bags. You would generally need three to five layers of paper (usually more of the thinner kind), and the best way to know you're getting complete layers is to use two colors of paper. 

If you're using newspaper, alternate unprinted paper, printed paper or advertising (any two will do).

If you're using paper bags or other brown paper, you could either find the white bleached type (more expensive), or use the same brown paper, with felt tip marker scribbled all over it to differeniate it from the plain brown layer.

Glues can be simple cooked flour + water, or a half/half mix of white craft (PVA) glue and water.

Sue

My students are 14-18 years of age.
The clay that we are using is rejected pottery clay.
The self-portrait modeling is going to be done by hand.