In 2015, the Italian parliament approved the law no. 107, named “La Buona Scuola” (“The Good School”), in order to boost the quality of organizational processes in schools. Among these, one of the most innovative was introducing a performance evaluation procedure for the nearly 7000 school principals of Italian public schools, from primary to college.From 2000 on, the legal status of schools principals in the public system have been set to the managerial level. However, no formal performance evaluation had been really performed before. In 2016, the INVALSI (the governmental agency for the evaluation of the national education system - http://www.invalsi.it/invalsi/index.php) was instructed to formulate a project aimed to: i) translate into concrete organizational procedures the goals dictated by the law; ii) train the evaluation teams needed; iii) monitor by an appropriate research design the outcomes of the new performance evaluation.The paper describes and discusses the training programme for assessors, the research design and some preliminary results.