1) BBC television game show 2) Classroom groan elicitor 3) It may make a pupil shrink 4) Surprise for students 5) Surprise from the teacher 6) Unanticipated questions 
Pop Quiz is a British television quiz programme that originally aired on BBC1 from 4 July 1981 to 28 December 1984 with a Top of the Pops special on 4 January 1994 hosted by Mike Read. It was then revived from 21 May to 9 July 1994 on the same channel but this time hosted by Chris Tarrant. It was revived again on Red TV from 14 June 2008 to 30 Aug...
[n] - a quiz given without prior warning
noun a quiz given without prior warning