Google Classroom has the ability to share pages to classes through a simple interface. There's a Chrome extension to make this easy, but there's also a way to embed a button directly into a web page. There's an example on this page - click it, and you'll see the option to share the link with any of your Classroom classes. Note that you'll need to be signed into a Google Apps for Education account to be able to do this.

To include this gadget, insert a gadget by URL, and use this address (it's case-sensitive, so copy and paste for best results):

        http://www.opensourceteacher.ca/Classroom_Share.xml

Here's the source code:
The gadget spec URL could not be found