Splash Math is an excellent site/iPad app has recently announced their summer program for K-5 to help prevent summer learning loss and prepare students for their upcoming school year. This is a free program and has students using the Splash Math program just 20 minutes a day. Splash Math is a very popular online/app that can be downloaded by individual grade or in a complete package of 1st-5th. Splash Math is aligned to Common Core Standards, can track student progress in real-time, and is self paced for each individual learner, and has lots of resources such as worksheets and more.
I highly recommend checking out Splash Math summer program by clicking here.
For more information check out Edshelf.