At Mental Floss, they've compiled a list of seven scientific advances that came about from school projects. The students, working either alone or in collaboration with a more experienced scientist, developed their respective projects into some significant breakthroughs in the different fields in which they worked.
I confess none of my science projects was ever going to be anywhere close to even a minor scientific discovery, unless it was how fast one could be completed when the previously-forgotten deadline loomed.
Whatever started growing in my ill-tended undergraduate refrigerator, on the other hand, was most probably unknown to science. Maybe that was for the better.