Schools are held more responsible for evaluating, quality assuring and improving their student assessments. Teachers' lack of understanding of new, competence-based assessments as well as the lack of key stakeholders' involvement, hamper effective and efficient self-evaluations by teachers of innovative, competence-based assessments (CBAs). While evaluating two CBAs in Agricultural Vocational Education and Training institutions, two interventions in the evaluation process aimed to tackle these problems were examined: (1) starting with explicating the CBA in the teacher team using a concrete explication format and (2) qualitatively involving key stakeholders (i.e., teachers, students and employers) in the evaluation of the CBA through mixed-group interviews. Quantitative and qualitative analysis, as well as stakeholders' perceptions are used to find indications for the added value of these interventions for evaluation and further improvement of the CBAs. Results show that external facilitation is needed to make both interventions work. However, under this condition, explicating the CBA led to more complete, concrete and shared understandings of the actual CBA among teachers and mixed-groups interviews resulted in more concrete and elaborate evaluations of the CBAs' quality and more ideas for improvement. Both interventions can facilitate building up elaborate, more valid and concrete arguments for CBA quality in self-evaluations, certainly in the case of evaluating innovative assessments. Lessons learned will provide guidelines for incorporating the interventions into other evaluations of innovative programs. (Contains 4 tables.)