According to Official Guinness Records,
The most people dry bobbing is 1,452 and was achieved by Olaf Palme Elementary School (Netherlands) in Drunen, Netherlands, on 15 June 2011.
Gingerbread was used for the attempt, one piece for each participant as required by the guidelines. The attempt was part of the school's 25th jubilee.
For a complete list of 2011 records, please visit 2011 Guinness Records in Netherlands.