Subject-Verb agreement with compound subjects

[Carol]

CJ:
> I guess my experience with teaching accusative and dative has been
> largely the opposite of yours. Generally, my students have little
> difficulty grasping the concepts, since they've already mastered the
> nearly identical concepts of direct and indirect objects. And I can
> generally teach all my students need to know about accusative and >
> > dative in under ten minutes.
> 
> --CJ
>
Carol responds:
If they already know about the concepts of direct and indirect
objects, there's no point (IMO) in throwing in the outdated
distinction between accusative and dative. The same form (objective
case) is used for both--*and* matches the names of the uses to which
it is put. Use objective case for objects (direct or indirect objects
and objects of prepositions), What could be simpler?

Ask almost any native English speaker to give you the dative or
accusative case of a particular English pronoun, and I almost
guarantee that you'll get a puzzled look and a "Huh?" in response.

Carol, noting that what is taught these days is standard usage, that
is, usage agreed upon by the authorities, rather than prescriptive grammar