Roberto,

    You're right and she's wrong, and the way to make that clear is to
talk about the role of the which in the clause it introduces.  It's a
relative pronoun, and it stands in for the word group it modifies.  If
you substitute those classes (what it modifies)  into the relative
clause, you get nonsense.  Those classes Constructiviist teaching is not
the primary approach.  She could rewrite the sentence so that which is
in a subject role, such as In those classes which do not use
Constructivist theory as their primary approach.  Here, it becomes even
clearer, also, that the semicolon is not being used well. In both cases,
it follows an introductory prepositional phrase (including a relative
clause modifier for the noun phrase object.)  This certainly defies
traditional advice.  I'm not one to advise against following all
traditional rules, but I can't think of a good  (functional) reason for
the semicolon here.
     If I'm confusing you at all, let me know and I'll try to make the
argument less technical.  You're initial instincts are absolutely right.

     Craig