You are perhaps referring to Building Bulletin 100- Design for Fire Safety In Schools Published by RIBA Enterprises (NBS is part of RIBA Enterprises Ltd), 15 Bonhill Street, London EC2P 2EA, on behalf of the Department for Children, Schools and Families, September 2007.
Section 3.1.6 covers Corridors and circulation areas and has words to the effect that The schools’ circulation routes will almost certainly be important for relaying information to the pupils by means of notice boards, or used as a display area for eg, pupils’ work. Notice boards should not be more than 3m wide, and there
should be a gap between notice boards on the same wall of at least 1m. Notice boards in a protected corridor should be fitted with a cover, preferably top hung so that the cover cannot be left ‘jutting-out’ into the escape route.
If you email me I may be able to help you with further information on where you may obtain a copy.