Background: This study focuses on a novel observational paradigm (SNAP) involving a rigged competitive card game (Murray, Woolgar, Cooper, & Hipwell, 2001) designed to expose children to the threat of losing. Recent work suggests that this paradigm is useful for assessing disruptive behaviour in young children (Hughes, Cutting, & Dunn, 2001). Method: We report on a large study (involving 800 five-year-olds) that compares observational ratings of disruptive behaviour on the SNAP game with mother and teacher reports of externalising behaviour on the CBCL and TRF (Achenbach, 1991a, 1991b). To ensure independence of data, playmates were randomly assigned to two different sub-samples. The validity of this rigged game for examining individual differences in disruptive behaviour was supported (in both sub-samples) by modest but significant correlations with both mother and teacher ratings of externalising problems, and by significantly elevated SNAP ratings among children rated by mothers and teachers as showing extreme (≥95th %) levels of externalising problems, compared with the remaining majority of children. Results: Significant gender differences in disruptive behaviour were found on all three measures: observational SNAP ratings and mother/teacher questionnaire ratings. Factors that may contribute to this gender difference are discussed. Conclusions: Our findings emphasise the importance of multi-method, multi-informant measures of disruptive behaviour, and suggest that the rigged card game used in this study is a valuable adjunct to more standard methods of rating disruptive behaviour.