This study was designed to investigate the understanding of proportion by a select group of college-bound adolescents. Gender-related differences and the influence of course experience were also studied in relation to first-order direct proportional reasoning and multiple proportional reasoning. The 901 subjects were administered the Tall-Short task as a test of first-order direct proportional reasoning. From the 474 subjects classified as successful, a random subsample of 128 subjects was administered the Projection of Shadows task. Only 22 subjects succeeded on all four subtasks of this multiple proportion task. An analysis of the transcripts of responses showed that feedback and second trials were essential for success for most (68%) of these successful subjects. In addition, this select subsample generally used a multiplicative strategy and still could not overcome the inhibiting effect of focusing on direct proportions. There were significant gender differences, in favor of male subjects, in first-order direct proportional reasoning but there were no gender differences in multiple proportional reasoning. Prior course experience in mathematics and science were each significantly related to first-order direct proportional reasoning but there was no significant relationship between either of these variables and multiple proportional reasoning.