"The universe had or has an intelligent designer." That is a scientific hypothesis, put forward by intelligent design. It is a rather stupid one, since it (obviously) cannot be proven or disproven by current scientific means, but it is a scientific hypothesis.
It can neither be proven nor disproven. Until it can be proven, by independent, replicable experiments which have been undertaken by several unrelated scientists, and there is enough evidence that a significant number of scientists say it is "probable" it cannot be considered a scientific theory.
We don't teach scientific hypotheses in science classes, we teach scientific theories and scientific facts. There is not enough evidence to support the hypothesis to make it a theory. Thus, it should not be taught in science classes.
Now, as a matter of faith, I believe there is an intelligent creator, G-d, who formed the heavens and the earth. However, I do not put it forth as a scientific fact, because it cannot be proven scientifically. I do not put it forth as a scientific theory, because there is not enough evidence to show it to be true beyond reasonable doubt. Anyone who does put forth intelligent design as a scientific theory or fact is either a liar or deluding themselves.