All 189 Canterbury primary schools were surveyed to determine the prevalence of children with behaviour disorders. Prevalence rates were estimated by sampling at Years 1, 4 and 7. A total of 186 schools participated in Phase' 1, which asked schools to nominate the number (if any) of children with severe behaviour problems currently enrolled. A total of 103 schools provided confirmatory information in Phase 2. For each child nominated two staff members were asked to complete separate copies of the Canterbury Social Development Scale. Nominated children who were scored at 140 or less on the Scale were counted. The overall prevalence was estimated at 4 - 4.5%. Prevalence rates were estimated for types of schools according to funding, administrative type and community, and according to their Targeted Funding for Educational Assistance (TFEA) rating from the Ministry of Education. The separate rates estimated for boys and girls revealed much higher prevalence among boys - a ratio of 5.6:1.