Have you heard of Kahn Academy?
It is an amazing (and absolutely free) resource for students, teachers, parents, and home school students on a variety of math and science skills. There are videos, tutorials and practice for math and science skills from basic addition and subtraction for elementary students to high school and college level math and science. I first saw this website while watching the news and immediately went to check it out. It is provided by Bill Gates and Google and I was amazed by the amount of material that was covered through the tutorials. It is a perfect summer resource for students (and your own little ones- I know I plan to share it with my daughter) and would make a wonderful addition to any classroom for additional support in math and science.
Go check it out and enjoy!