Community college developmental math students (N = 657) from three math levels were asked to place five whole numbers on a line that had only endpoints 0 and 20 marked. How the students placed the numbers revealed the same three stages of behavior that Steffe and Cobb (1988) documented in determining young children's number sense. 23% of the students showed a lack of the concept of part-whole coexistence in this task. In two of three levels, lack of the concept was found to be significantly related to success (final grade of A, B, or C) in developmental math.