A democratic school is a school that centers on democratic principles and participatory democracy with “full and equal” participation from both students and staff.

Democratic schools position youth voice as the central actor in the educative process by engaging students in every facet of school operations, including learning, teaching, and leadership. Adult staff support students by offering passive and active facilitation according to students' interest.

Another tenet of democratic schools is giving students the power to choose what to do with their time. There are no required classes, and sometimes there is no requirement to take classes at all. Students are free to choose an activity that they desire, or feel the need to do. They are free to continue activities for as long or short a time as they see fit. In this way they learn both self-discipline and self initiation. They also gain the advantage of the increases in both learning speed and learning retention that accompany engagement in an activity that one is passionate about. The students at these schools are responsible for and empowered to direct their own education from a very young age.

You can get a list of democratic schools in the US here.