Quality models for online and blended learning (OBL) have mainly been developed in higher education. The literature indicates that these models are often conceptualised from the providers' perspective. What is important for the quality of OBL from the students' perspective has recently received increased attention in the literature. Consensus among stakeholders about students' quality needs is useful to support dialogue between professionals to strategically adopt OBL and to ensure that the needs of students are met. This study aims to validate a quality instrument for OBL, taking a set of 74 quality indicators and analysing them in terms of seven success factors (credibility, accessibility, transparency, flexibility, interactivity, personalisation, productivity). The Delphi method was selected as most suited. Participants from adult education were asked to indicate on a 7-point Likert scale to what extent the indicators add to OBL quality to meet students' needs. After four Delphi rounds, the participants agreed on definitions of success factors and 30 indicators. The results are useful for institutions, ministries of education and external quality assessment agencies to assess the quality of OBL and can support institutions to implement improvement actions to ensure that the needs of students are met.