This chapter presents the results of a small-scale research study on the number knowledge of students with Down syndrome in Indonesia. Five students with Down syndrome and ages ranging from seven to 19 years, from a special education school in Yogyakarta city, were interviewed to document their abilities in identifying numerals, solving number problems involving the use of unscreened and screened collections of counters, and solving one-digit and two-digit number problems in horizontal format. The approach and the schedule of assessment tasks in the interview were adapted from that used in Mathematics Recovery (Wright, 2008). The interviews were conducted individually and videotaped in order to capture subtle clues related to students’ abilities. The number knowledge of the ﬁve students with Down syndrome is described, compared, and discussed.