This feature is only available on the Teach Your Monster hub site and the Reading for fun and Number Skills games.
To do this you will need the player name, password (if set) and class code of the player you wish to add to your account.
For linked players:
You will not be able to edit their name, details or stage of the games
You will be able to see their progress information and stats
Teach Your Monster hub site
Go to 'add player' at the bottom of your player list
You will be taken to this screen, go to the bottom and click 'add existing player'
Enter the player details
Press Ok and the player will appear in your list with a star.