This paper presents the development of a formative assessment ontology, called OntoNoteF, that enables teachers to add a formal semantics to formative feedback annotations they put on students’ lab reports in LabBook system. It is linked to a learning domain ontology enabling teachers to give formative feedbacks to students on expected lab work tasks. OntoNoteF is developed following a rigorous methodology, from teachers’ requirements to the ontology implementation in MemoNote annotation tool. Its implementation in MemoNote permits to provide new features that can help teachers to annotate students’ lab report easily and to identify common errors.