Teacher rating scales are an efficient, practical way to gather information on children's behaviour problems in school. Previous research has reported on agreement between parents' and teachers' reports, but less attention has been paid to inter-teacher agreement in young children, to the distinction between relative and absolute agreement, or to variability in teachers' agreement. In the present study, 26 United States teachers of three- to five-year-olds reported on the behaviour of 132 children in their classrooms, with the widely used Achenbach Teacher Report Form. Stronger agreement was seen on ratings of externalising than internalising behaviour. Absolute agreement was not always high even when teachers showed close relative agreement. Agreement varied significantly across informant pairs, suggesting that some teacher pairs rate children's behaviour in very similar ways, while others agree very little. Agreement was stronger in higher-SES than lower-SES classrooms. (author abstract)