This is going to depend on how you set their drive sharing settings. Sites are treated as drive files as far as sharing privileges go. Our school does not allow students to share with users outside the domain, which means that any site they made would not be available to the public. We actually have site creation turned off for students but have given them the ability to edit already existing (domain) sites. Teacher's are responsible for creating (and deleting) any sites they want students to work on, meaning they can be made publicly viewable if desired.
