Assessment is an essential resource for guaranteeing quality education. In order for it to be effective, it must be continuous, formative and adapted to the characteristics of the individual student, so that it shows their abilities. Students with Down Syndrome benefit from these aspects, as they can demonstrate their achievements and difficulties in different ways. This article analyses these approaches and brings together the suggestions of 14 experts, in the field of education for students with Down Syndrome, from three different countries, 5 members of Belgium and Spain, and 4 members of Ireland. Through the instrumental case study and focus discussions of the experts, using the Delphi method, a series of basic aspects are established on the most appropriate methods and evaluation tools for the target group. In the analysis the experts agreed on three key aspects (with scores of three out of three): maintaining high expectations of students' potential, encouraging self-evaluation, and enabling students controlling their own learning process. The group of experts proposes the use of a learning register or portfolio as a method of assessment for students with Down Syndrome.