Man this thread is growing faster than I can read it. Ok, the reason Darwin's Theory is taught is simple. Science pure and to the core. Darwin's Theory is based on his observations and collected data. It follows in the basic principles of science. If you follow Darwin's work you will find that he makes no broad leaps in the actual collected observations. Granted the interpretations to species and patterns can be called into question since they are treated as truth through similarity. The reason Darwin is taught though is because of the premise behind his methods and his search for an explanation through observation, collection, and correllation.
Inteligent Design would be given a fair chance in schools if it had sufficient scientific backing behind it and was able to provide a concrete display of the scientific research principles behind it. As this particular case was handled, forcing teachers to mention a theory without any physical evidence whatsoever goes against the very heart and soul behind science.