Two experiments are reported which demonstrate the development of co-ordinated description languages in two groups of communicators playing Garrod and Anderson's (1987) maze game. The experiments contrast language co-ordination between speakers who always interact with the same partner (isolated pairs) as compared with speakers who interact with different partners drawn from the same community. Whereas the isolated pairs show higher degrees of inter-speaker convergence than the community pairs at the start of the experiment, the situation reverses by the time they have all played six or more games. The results are discussed at two levels: (1) in terms of Lewis's formal theory of conventions, and (2) in relation to a language processing model which abides by the "output/input co-ordination" principle proposed in Garrod and Anderson (1987).