Two of my favorite Google Extensions are Tab Scissors and Tab Glue. These two extensions allow you to split apart your tabs into two equally sized screens, or glue them back together into one. This works with any tabs you want to display side by side.
Alice Keeler, one of my favorite ed tech educators (check out her blog!), has just started creating her own Google Extensions and Add-Ons. Her newest, Gradebook Split, allows you to click on her extension, and a new tab with your gradebook will automatically open, splitting your screen. This extension will make it so much easier to grade your student work. You will need to enter in your gradebook URL in the settings for the Gradebook Split extension. Check out Alice's blog for more information about how to use Gradebook Split and a video demonstration.
Notes about using Gradebook Split with School Loop: If you have multiple gradebooks in School Loop, you can only choose one of your gradebook URLs to enter into the extension. Also, you must be logged in to School Loop when you click on the extension, or, it will prompt you to log in first.