This research occurs in a specialized primary school for students having emotional and behavioural disorders (EBD) in a suburb of Montréal in Canada. The aims were to a) evaluate the impact of a schoolwide de-escalation intervention plan on the use of de-escalation and seclusion-restraint measures throughout the school year and b) to identify the precursors of seclusion and restraint use (SRU). Data were obtained from systematic observation of behavioural incidents over a period of three months. The frequency, the duration and the nature of behaviours were observed. Results showed a higher frequency of de-escalation measures compared to SRU. They also showed a significant decrease in the frequency and the total duration of SRU throughout the year. A high frequency of negative behaviours was observed among students and SRU was found to be significantly higher in younger students. Implementation of a behavioural support plan was found to promote self-regulation and prevent SRU in students with EBD. Young students and those with aggressive behaviours seemed to benefit more.