Police say they are working closely with the school following the incident on Monday 10th December.
Officers were called into St Michael's C of E in Heavitree on Monday.
The knife was not taken out of the child's bag until it was confiscated by staff at just after 9am.
Plymouth man jailed for child sex offences
Peter Lamble, 47, gets 6 years
£5 Council Tax Hike for Devon Firefighters
Tax rise to plug service gap
Exeter's 'most deprived area' to get new leisure hub
'This is a fantastic opportunity'
Bay budget includes new fund for deprived communities
Council tax to be fixed below limit set by government
Major Newton Abbot projects 'on target'
'Now the heavy work is about to start'
New estimates suggest council reorganisation could cost £50 million
Some figures say it could be higher
