It is for students third grade on up that provides instructional videos for concepts in mathematics, science, social studies, and the humanities. For elementary teachers, this would provide opportunities for differentiated instruction as students can independently learn and master concepts above or below grade level.
Teachers could implement this two ways. First they could just send recommended videos to students when they need to supplement a lesson. Second they could create student accounts and monitor students progress as they participate in Khan Academy. If you are interested in creating student accounts and managing/monitoring student progress through the site, Khan Academy provides an entire list of things to do to get through the process.
Check out the website. If you have an iPad, check out the app.
Let me know if you want to jump into it.