If you're trying to open the ConnectED link through Canvas on the iPad, it might be showing a blank screen and not opening anything. This is because Safari changed the way it handles popups with the last software update. You need to make a change in Settings to allow a link to launch a new window.
Note that this only applies to Safari on the iPad. If you or your students are using Chrome, you're prompted to allow the popup to launch without making any other changes.
In the iPad Settings, find the Safari options on the left. Then, find Block Pop-ups on the right and turn it off.
When you launch ConnectED in Safari, you will be prompted to allow the popup which will then open the McGraw Hill site.