Developing rating scales for assessing interactional performance is demanding since it is a relatively complicated procedure. The present study investigated the psychometric characteristics of the CAP rating scale (Wang, 2015) for assessing interactional competence at micro-level. To this end, 160 Iranian intermediate EFL learners were selected based on their performance on TOEFL iBT test from a language institute in Tabriz. Four interaction tasks were used to elicit students’ performance on interactional competence using the CAP rating scale. Five raters were recruited in the study to assign score to each individual’s performance. The participants were pretested and post-tested at the beginning and the end of the term through the same scale. The Pearson correlations were computed in order to estimate the test-retest reliability indices of the scale. In addition, five separate exploratory factor analysis (EFA) through the varimax rotation method were conducted in order to investigate the underlying constructs of the communication functions individually and as a total. The results revealed that the CAP rating scale enjoys a reasonable reliability indices and the four functions i.e. building argument, developing discussion, offering support, and shaping connection can be appropriate predictors of interactional competence. Some pedagogical and assessment implications are presented as well.
