I don't have very fond memories of watching video in school, it was great because we didn't have to do anything, but that was it. When I had the choice I would never have watched something that described itself as "educational video". Now I work in educational video and perhaps it's not surprising that it has such lowly status.
I suppose that as an adult and filmmaker the DVD commentary on The Godfather, for example, was an educational video.
What great video have you seen that has aimed to teach you something and succeeded?