Abstract : Our work deals with teachers' activities instrumentation within the framework of mediated tutoring. In this context, we want to provide teachers with information in order they better manage their activities. We conducted a theoretical study that allowed us to identify two main teachers' activities. Indeed, as well as regulating learners' activities, teachers have also to regulate their own tutoring activity. From this study, we designed TEAMO (Teachers' Activities Model), a description model of processes related to the activities that teachers have to manage at the same time during learning sessions.Based on TeAMo, our proposal is to provide teachers with detailed information about the effects of their interventions through an Indictor-Based Approach. This approach is twofold: first, in order to support the regulation of learners' activities, we supply teachers with indicators which reflect these activities quantitatively and qualitatively . Second, in order to support teachers' self-regulation, especially their interventions, we provide them with meta-indicators (indicators which follow the trends over time of other ones) which allow to measure the effects of their interventions.The indicator-based approach has been implemented in the TEL system Hop3x. We conducted several experimentations by using Hop3x, in the field of object-oriented programming. These experimentations allow us to validate our proposal. Indeed, experimental results show that supplying teachers with information about their interventions improves the effectiveness of these interventions in a quantitative and qualitative ways. Moreover, these results also highlight that the improvement of teachers' performance has a positive influence on learners' performance.