Online and blended learning (OBL) is valued, but it also offers challenges. Literature indicates that OBL can enhance access to education and increase flexibility for students. However, the reported dropout rates indicate that student participation in OBL programmes is a concern. Scientifically valid knowledge about how factors that help students participate in OBL are related to student participation is necessary for quality improvement of OBL. This knowledge can help professionals determine what they need to improve in their institution and how to prioritize those improvements. In this study, we report on the validation of a quality instrument with indicators related to quality dimensions present in quality management frameworks and important success factors that aid student participation in OBL. These success factors are as follows: credibility, transparency, flexibility, accessibility, interactivity, personalization, and productivity. The partial least squares structural equation modelling (PLS-SEM) method is suitable for validating complex models in studies where predictive accuracy is important. According to adult students, all success factors, except flexibility, are important for aiding OBL participation. Adult students perceive that the quality dimensions of learning activities and student support (related to interactivity) deserve priority in improving participation in OBL in adult education.