Frequent feedback should be sought by professors and departments on students' opinions about the quality of education they're receiving. Feedback surveys are often done once at the end of a semester for most departments but should be done continuously during the semester so lecturers can adjust their teaching methods if required. If possible, questions should be answered about individual lecturers to assure that no lecturers are slacking on their teaching work to further their time spent in research.
Companies exist to carry out these surveys (https://www.panoramaed.com/surveys) and can be utilised to achieve these improvements in student education. The SU should approach schools/departments with this a way of departments improving/validating their quality of education.