Forest is a really cool Chrome extension to help teachers and students focus

Forest is a free Google Chrome extension designed to help you focus and not get distracted by Internet sites. Once installed, you can click on the icon to plant a tree and have it start to grow. Under the options you can blacklist and whitelist websites. The blacklist is to list sites that will distract you. For schools, the whitelist option would probably be better, where students list the sites that they need to use. I whitelisted google.com, and then was only allowed to use Google sites without killing my tree. ¡¡Once you tree starts growing, you have to work for 25 minutes. Clicking on the extension will show encouragement to continue. If you visit a blacklisted site, Forest blocks the screen.

You can Give Up and access the site, but it will kill your tree.

Unfortunately for students, while the extension is free, doing anything with your trees or forest requires a purchase through the smartphone app.