I have taken two workshops in encaustic. In one, we used wood and masonite.
In another, we used several different varieties of paper.
Are you fusing the wax if you are applying more than one coat? (That is,
heating it really quickly to briefly melt the wax.) Fusing is supposed to
allow you to apply layer upon layer of wax. In the workshop, we used a
propane torch. I realize that may not be practical in a school setting, but
we also used a griddle and put our pieces on the griddle. I have a heat gun
that rubber stampers use for embossing and discovered that it does the job