HI - Try Stylus Studio. The main advantages of using it for teaching
purposes are 2-fold:

(1) you can use any XML processor (MSXML, .NET, Apache Xalan, Apache
Xerces, Saxon, XSV, DataDirect XQuery .. or whatever). I have found
from personal experience in  teaching XML classes, that the students
come from different technological backgrounds, so support for
C++/Java/.NET processors is a plus.

(2) The XML Schema Editor (
www.---.com ), XSLT Editor (
www.---.com ),  and XQuery Editor  (
www.---.com ) all provide
synchronized graphical editing views and text editing, so students can
edit the code and at the same time, see a visual representation of what
they are working on, this is the same intuitive approach used by tools
like dreamweaver/frontpage for HTML editing.

A free trial is available here:
www.---.com
There are some academic discounts here:
www.---.com
And, here is a marketing piece that talks about 10 reasons why schools
use Stylus Studio to teach XML:
www.---.com


Hope that helps.

Sincerely,
The Stylus Studio Team
www.---.com