validate .xml against .xsd

I would like to validate a .xml file against a valid .xsd file.  What tools
are recommended for this purpose.  I have tried XSV and it will validate
that the xml is well formed, but it does not complain if the xml breaks
constraints of the xsd.  Maybe I am running it wrong, but I have tried
everything that I can find.  Always see validation='lax' in the output.  Is
this the problem.  How can I make it strictly validate?  Any help on this
would be appreciated.