The link below will take you to a wonderful website for students. The website will be useful for any upper elementary school student to use or consult when studying the phases of matter. This website has a nice and easy to use index on the right side of the screen and once you click on something you will be taken to a wonderful page with easy to read information as well as nice pictures to help one to better understand the information they are reading. 

http://www.chem4kids.com/files/matter_intro.html