This paper reports on the mathematical modelling of four classes of 4th-grade children as they worked on a modelling problem involving the selection of an Australian swimming team for the 2004 Olympics. The problem was implemented during the second year of the children's participation in a 3-year longitudinal program of modelling experiences (i.e., grades 3-5; 2003-2005). During this second year the children completed one preparatory activity and three comprehensive modelling problems. Throughout the two years, regular teacher meetings, workshops, and reflective analysis sessions were conducted. The children displayed several modelling cycles as they worked the Olympics problem and adopted different approaches to model construction. The children's models revealed informal understandings of variation, aggregation and ranking of scores, inverse proportion, and weighting of variables. (Contains 1 figure and 1 table.) [For complete proceedings, see ED496859.]