The purpose of this study was to determine whether or not decreased articulation of speech played a role in the ability of an individual with Down syndrome or Fragile X syndrome to signal noncomprehension and whether the two groups differed in their levels of articulation of speech and noncomprehension signaling ability. The research was conducted using a group comparison design with two independent groups. The independent variable was the diagnosis of either Down syndrome or Fragile X syndrome, and the dependent variables were articulation of speech and noncomprehension signaling ability. The study was conducted in New York, New Jersey, Connecticut, Massachusetts, Delaware, Maryland, and Virginia, with 36 male participants, 18 each with Down syndrome and Fragile X syndrome. A screening assessment confirmed that the participants could hear within normal limits and that they were able to sit and attend, and follow simple directives. Performance on a receptive and expressive language assessment indicated that the groups did not differ significantly in their vocabulary and language abilities. The dependent variables of primary interest included number of errors on an articulation test, given to determine quality of speech for each participant, and number of noncomprehension signals on a noncomprehension signaling task, which was administered to determine if the participants could ask for clarification when unclear directions were presented to them. Results indicated that there was a significant relationship between articulation of speech, as measured by articulation errors, and noncomprehension signaling for both groups combined and for the DS group, but not for the FXS group. Results also indicated that, although articulation of speech was not significantly different in males with DS and FXS, males with DS were more likely to noncomprehension signal than males with FXS. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://www.proquest.com/en-US/products/dissertations/individuals.shtml.]