Hi there!

I'm afraid there's no way to hide or restrict access to certain courses on the site---all users are able to access all of the courses and site content in any order.

However, you can change the courses that are listed on his Learner Homepage, which may help limit navigation to other courses on the site. You can find instructions for modifying his courses here: https://support.khanacademy.org/hc/en-us/articles/115003342971-How-do-I-edit-the-My-Courses-section-on-my-Home-page-

Please note that this must be done while logged into his account---there's no way for you to modify the My Courses menu for him via your own account.

I hope this helps! Please let me know if there's anything else I can do for you!