The question "Why not?" following the statement "Philosophy classes have no place in high school anyway" is not fallacious in any sense of the word, so don't get your knickers in a knot. I was a philosophy major in college 30 years ago, so I have more than a passing interest in the topic.
I had read a good bit of philosophy prior to going to college and had little trouble understanding the major philosophical questions that I would study in more detail in the 4 years that followed.
I think the poster who suggested an elementary logic class was spot on, but for high schoolers to recognize that the systems of thought in evidence around them go back to ancient times is a good thing. Provides some much needed perspective. Questions of free will/determinism or issues of metaphysics/materialism are in no way beyond the abilities of a high schooler.
Did Dewey introduce anything new or lasting with his pragmatism?