All schools are educational institutions. Some colleges are educational institutions. However, we are not finished yet. We must now add the assumptions that the premises make about the sets referred to in their subject terms. Here this means that we must place a capital X in the area that represents colleges that are schools, since this is implied by the second premise.
All colleges are schools.
All schools are educational institutions. Some colleges are educational institutions. Normally, we would also have to place lowercase x's, connected by a line, in the two areas where schools and educational institutions overlap, since this is an assumption that the first premise commits us to. Here, however, since the second premise already commits us not only to the existence of some colleges, but also to existence of some schools, this is unnecessary. Clearly, our diagram shows that the argument is valid on the classical view.