This chapter reports on the Portuguese trial of the Environmental Rating Scale for Sustainable Development in Early Childhood (ERS-SDEC) which was carried out in the context of the initial training of pre-school teachers at the University of Évora during their practicum in local pre-schools. The context of this trial in initial teacher education provides a particular focus on the professional development of the students and the cooperating teachers provided by their engagement in a collaborative action-research project that was focused on Education for Sustainable Development (ESD). After providing some Portuguese contextual elements related with ESD, we will report on the trial of the scale in Évora and its results in terms of improving the quality of classroom practices and students’ and teachers’ professional development provided by their participation in the project. Finally we will share some refl ections on the project, the format and use of the scale and issues that we learned to be critical in terms of ESD in early childhood.