This study examined the effects of participation order and group size on discussion training of the autonomous dialogue, which means communication skills for discussing spontaniously without third person's help in a group of about 6 members. Measures for the effectiveness of discussion were self evaluation on rating scales. Participants were 89 undergraduates. They rated their own and others' discussion in 7 dimensions: honesty, equity, activeness, diversity, depth, management, and cumulativeness. As a result, the activeness component was most facilitated when the students participated after observing others' activity under the condition that their group size was kept in 6 members all through the sessions or increased gradually. The management component was most enhanced under the condition that their group size was increased gradually.