No, it is not. Copyright Law does not allow the transfer of formats (e.g. VHS to DVD) without permission of the copyright holder, EXCEPT for the limited provisions of Section 108 of the copyright law.
Individuals are prevented by copyright from making DVD copies of copyrighted tapes that they own. Use of such copies in the classroom is most definitely illegal.
Digitization and streaming of tape copies without license or permission is not permitted either.
"Reproducing a VHS to DVD without the prior permission of the rights-holder is an infringement of copyright. This kind of reproduction is not exempt because it is not “fair use” as defined in Section 107 of the Copyright Code and it does not qualify as a lawful reproduction under Section 108 of the Copyright Code."
Sources: American Libraries, The Magazine of the American Library Association
§ 107. Limitations on exclusive rights: Fair use
"The fair use of a copyrighted work, including such use by reproduction in copies or phonorecords or by any other means specified by that section, for purposes such as criticism, comment, news reporting, teaching (including multiple copies for classroom use), scholarship, or research, is not an infringement of copyright."