Clearly that has been overtaken by a new meaning now, but I believe there is an instance in one of the Sherlock Holmes novels as well with Holmes waking up Dr Watson by knocking on his door at night and apologizing for knocking him up.Hmm, I just looked it up. It seems British uses this term in that sense, knocking on someone's door. So I guess the other meaning is more of an Americanism? My teacher just thought it was amusing, and a lesson in regional slang.