One interesting occurrence that happened when I started having a class website was that students would actually read the interesting articles I would post on my site or tweet out. I did not assign them or even talk them up, I just told my students about the fact that I would be posting them from time and time and they might find them interesting. I tried to find articles or resources that were somewhat related to what we were learning in the classroom but also that were at their level or close to.
Imagine doing something similar for your students over the summer where you find a way to post articles or resources that students might find interesting and would keep the learning going over the summer months. You would not have to assign this but just make the students aware of this during the school year and make it so they can get to them easily. You could post to a site or just use Twitter to share out the resources and articles. Keep adding new resources and articles over time so that there is something new when they come back to check the site again. I think many would be amazed at how many students would actually look over this over the summer and this could help diminish the so called “summer slide”. I still have former students of mine who follow me on Twitter who comment on articles I still post, even up to 7 years after they had me as a teacher.