Children who don't read during the summer vacation don't do well on reading comprehension tests when school resumes. The cumulative effect can be devastating: summer non-readers can end up two years behind their peers by sixth grade. By contrast, children who read four or more books over the summer fare much better academically in the fall than their peers who read only one book or no books. The Massachusetts Board of Library Commissioners is challenging people of all ages to read four or more books this summer. So what's your four? Here are mine, chosen from my unread shelf. Promote this campaign on social media with the hashtag #WhatsYourFour And tell us: what are your four?