The man, aged 41, was held on Wednesday on suspicion of possessing cannabis and child neglect (exposure to harm) before being released on bail until a date next month.
A 24-year-old woman was arrested over the same offences on Thursday and is being held in custody at a north London police station.
Police were called by London Ambulance Service at about 11.45am and 17 pupils were taken to hospital as a precaution. None of them were seriously ill.
The investigation continues.