But theories by definition cannot logically be proven; they can only be disproven. Almost everything in science is a theory (notice how I didn't preface that with "only a"), and will forever remain a theory. If all theories were so labelled, including such well-established models as the circulatory theory of the blood, or the theory that rain is condensed from atmospheric water vapor, the caveat would cease to mean anything to the students.
You raise a good point... so, theoretically (tee hee) could we then call Creationism a Theory, since it can't be proven, and it hasn't really been disproven? Thus, it is, in a way, just as valid as the theory of evolution??? ;0)
My own opinion is, some higher power used evolution as the vehicle for creation, but that's just me ;0)