This website has all of the standards that 4th graders are expected to learn. You can click on any subject and it will give you on-line games and activities. http://www.internet4classrooms.com/skills_4th_original.htm
Try these websites for games and experiments. Lots of fun!! http://www.highlightskids.com/
http://www.funbrain.com/
If your child has a project or just wants to dig deeper on a topic they enjoy, then this is the website for you. http://cybersleuth-kids.com/
A reading website with games in both English and Spanish. http://www.rif.org/kids/readingplanet.htm