Police used CS spray during the arrest of a 14-year-old boy at a school in Northern Ireland.
An independent investigation has been launched into the incident at Oakgrove Integrated College in Londonderry on Tuesday afternoon.
The teenager was released on bail pending further inquiries, a PSNI spokesman said.
The spray is generally used by officers to control aggressors in situations where lethal force is inappropriate. It can cause streaming eyes and a burning sensation.
Figures on the PSNI’s use of the substance noted 479 cases in 2008/9, including 28 involving members of the public aged 17 and under.
Police Ombudsman for Northern Ireland Dr Michael Maguire investigates police behaviour, although usually following a complaint.
His spokesman said: “The Police Ombudsman has decided to call himself in because he believes that this incident merits an independent investigation.”