The ``Proyecto Educativo con Telescopios Robóticos'' (PETeR) of the Instituto de Astrofísica de Canarias is an online inquiry-based laboratory that allows school students to carry out their own observations and research projects in astronomy using professional robotic telescopes. The availability of observing time on several telescopes, which also offer different types of observations through user-friendly portals, has allowed us to open the project to the entire Spanish educational community, from primary to secondary school and vocational training. This paper outlines the project's goals, materials and educational approaches used, as well as the teacher training programmes we provide in the framework of PETeR.