The Group Test of Openness (GTO) is comprised of 24 behavioral items that represent, in equal numbers, three different levels of openness. Participants (N = 69) obtain a score by selecting to perform 6 items, which are summed in terms of their openness levels. The GTO was shown to have a moderate degree of stability. It does not appear to be highly reactive. Predictive validity was demonstrated through a 14-week high school course in counseling skill in which scores on the GTO increased in the treatment group but not the control group. The advantage of the GTO over other measures of openness lies in its focus on behavior within a group and on its objective methozof scoring However, it is noted that any measure based on the openness value of specific behaviors may require recalibration for certain populations.