All schools are educational institutions. No schools are bars. Some bars are not educational institutions. Now, however, we need to add the additional assumptions that the classical view makes about the premises. Since the first premise commits us to the existence of at least one school that is an educational institution, we need to represent this by placing a capital X in the unshaded area where schools and educational institutions overlap.
All schools are educational institutions.
No schools are bars. Some bars are not educational institutions. To represent the presuppositions that classical logic makes about the second premise, we must also add in our diagram that there exist some schools that are not bars and some bars that are not schools. However, we have already represented the first of these assumptions in the diagram. So all we need to do, then, is to represent the assumption that some bars exist that are not schools.