In the context of a general research question about the effectiveness of computer-based technologies applied to early music-harmony learning, this paper proposes a web-based tool to foster and quantitatively measure harmonic awareness in children. To this end, we have developed a web interface where young learners can listen to the leading voice of well-known music pieces and associate chords to it. During the activity, their actions can be monitored, recorded, and analyzed. An early experimentation involved 45 school teachers, whose performances have been measured in order to get user-acceptance opinions from domain experts and to determine the most suitable metrics to conduct automated performance analysis. This paper focuses on the latter aspect and proposes a set of candidate metrics to be used for future experimentation with children
