I had the reverse happen to me in Silver when I taught my Alakazam Shadow Ball thinking it was going to wreck everything because Mewtwo used it in the movie so its probably good for psychic types but only did tickle damage off of Alakazams pitiful attack. Thats what helped me learn about the physical-special split.
I'll tell you where the real road lies: Between your ears, behind your eyes. That is the path to Paradise, and, likewise, the road to ruin.