Basically these are students in their final two years in an English secondary school. These two years are non-compulsory, (for more info on what a sixth form is see the specific node). Sixth Formers generally enjoy certain privileges that other students do not. For instance I am currently typing this node in the sixth form IT room, adjoined to the sixth form common room (a hallowed space in which only a sixth former may enter). I could not do this in the lower school. Privileges are different between schools, In my school they are:

Uniform is no longer compulsory (and therefore not worn at all, ever)

Priority at lunch (allowed to push in the line in front of lower school pupils

Free periods

Allowed to use teacher’s first names

Allowed off-campus when not in a lesson

Allowed in the sixth form common room, including use of sofas, stereo and coffee machine1

Sixth formers are revered by the rest of the school as demigods. Although they have no official authority, it is generally excepted that if you are in lower school and a sixth former tells you to do something, you do it. The car park/playground/courtyard/alternative-classroom area can be packed with year 7-11s and yet when a sixth former walks through they will part, like the Red Sea for Moses. (yeah... I wish)

In all being a sixth former is pretty sweet!

1Bastards got rid of the sofas and coffee machine in my final year.