The following web site will take you to the official DoD policy governing the Voluntary Education Program:
The Department of Defense, through the various military services provides Tuition Assistance (TA) to current military students (Active duty, Federal Reserve Forces, and the National Guard). Please note: not all states offer TA to their respective National Guard forces.
For a service-wide overview: http://www.militaryonesource.mil/voluntary-education?content_id=268274
Military.com offers a useful quick source to Tuition Assistance.
Specific Service Education Sites: