Answer:
Creationism IS taught in public schools.
There are many forms of creationism taught in mythology classes.
Creationism, itself, is explored in philosophy classes.
Biblical creation is taught in English and literature classes.
Musical interpretations of Genesis are taught in music classes.
Creationism is not taught in science classes because it is not supported by any scientific evidence whatsoever. It makes no verifiable predictions. It also has no practical application.