You can upgrade your student account to one that allows private repositories using the GitHub Student Developer Pack. For more info, head to this link:
https://education.github.com/pack
Thanks very much to Mike for pointing me to this. (I now remember having seen this in the past but I had completely forgotten about it!)
Once you have upgraded your account in this way, I would appreciate it, if you would convert your homework 1 repository to a private repo. Thanks!