Configuring Limit Web:
Click on the drop-down arrow to the right of the Limit Web button in the toolbar.
Select Configure Web Limiting... 
Select the Web Limiting tab.
Select Allowed Web Sites and add website addresses to those lists. Any sites that are not listed in the Allowed Web Sites list will be blocked. You can add additional sites to this list if they are needed for curriculum and students are blocked from accessing them.

Once the allowed list has been configured, make sure to highlight all student computer and click the dropdown arrow next to web limited. Make sure “Allow list” is checked.

Adding Websites to the List:
When adding websites to the Allowed or Blocked lists, start by entering only the site's domain name to allow or block the entire site (e.g. facebook.com, google.com).
Entering a more specific website address (e.g. mail.google.com, en.wikipedia.org) will only block or allow that specific part of the website.

There is a 30,000 character limit or 1400 bytes.
Examples:
Add to Blocked Sites: facebook.com  Result: All parts of facebook.com will blocked.
Add to Blocked Sites: mail.google.com  Result: All parts of mail.google.com will be blocked, but docs.google.com will be allowed
Add to Allowed Sites: docs.google.com/document/d/1llCNxxxxx  Result: This specific Google Doc link will be allowed. All others will be blocked.

Start by adding these sites, which are used in the curriculum. Other sites can be added as needed with the method shown above.

http://eepurl.com
http://homestyler.com
http://solarcooking.org
http://youtube.com
http://www.nps.gov
http://www.skyscrapercenter.com
https://appinventor.mit.edu
https://arcade.makecode.com
https://arduino.cc
https://bridgedesigner.org
https://cdn.sparkfun.com
https://code.org
https://code.makewonder.com
https://digilab.dremel.com
https://docs.google.com
https://mail.google.com
https://drive.google.com
https://helpx.adobe.com
https://kb.vex.com
https://learn.sparkfun.com
https://makecode.microbit.org
https://makeymakey.com
https://ozobot.com
https://ozoblockly.com
https://us.arckit.com
https://vectr.com
https://www.animationish.com
https://fablevisiongames.com
https://www.arduino.cc
https://www.arckit.com
https://www.arcgis.com
https://www.creativelearningsystems.com
https://www.fablevisionlearning.com
https://www.fabmakerstudio.com
https://www.fischertechnik.de
https://www.reallusion.com
https://www.sciencebuddies.org
https://www.sketchup.com
https://www.tech4learning.com
https://www.techsmith.com
https://www.thinkfun.com
https://www.tinkercad.com
https://www.vernier.com
https://www.wixie.com
https://zoom.us
https://teamviewer.com