Robin,
If it's in your budget, self-hardening (air-dry) clay might do for the
end of the week, or air dry your earthenware clay and let the students
seal it with white glue or a gloss medium when they get it home and it's
dry. This is good if they do thick sculptures - heads or animals that
might be risky to fire anyway because of drying and air bubbles.
Pre-fired tiles 6 x6" to paint on, with underglazes could be done
Thurs., and fired overnight.
Have fun ! Grace