Previous research in the area of children's knowledge of number agreement morphology has yielded mixed results. Some researchers have found evidence for sensitivity to agreement morphology at as early as 16 months, while others report that children do not comprehend number agreement morphology until as late as five or six years old. Studies of children's production of these forms suggest that while children go through a period of optionally using agreement morphemes as part of the Optional Infinitive stage of development, they show productive use of these morphemes at age two. Therefore, some researchers have concluded that this is an area of the grammar where production precedes comprehension. This general pattern of findings has several possible explanations, three of which will be described here. The general goal of the current study was to provide new information to this area of inquiry, with a particular focus on children's comprehension of "is" and "are" as well as plural -s marking on nouns. To address possible methodological issues with picture selection and looking-time studies, a manual search task was used to tap receptive knowledge of these forms. Forty-eight 30- to 36-month-old children were tested on their receptive knowledge if "is," "are," and singular/plural distinctions on nouns. Additionally, these children were given multiple assessments of their language production abilities and their non-verbal mental abilities. Results indicated that two-year-olds can comprehend noun morphology indicating number, but failed to show comprehension of "is" and "are." Additionally, when provided with both noun and verb information, the presence of the verb provided no added benefit to the children in terms strengthening their interpretation of the verbal prompts, suggesting that noun information regarding number is sufficient for sentence interpretation in two-year-olds. Analyses of relationships between production abilities and receptive knowledge of verb morphology found no correlations between these sets of variables. These findings contribute new information regarding the development of receptive knowledge of noun agreement morphology, and contribute new data to the ongoing debate regarding the development of sensitivity to and comprehension of verb agreement morphology. Methodological issues are addressed and potential theoretical implications of this work are discussed. [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.]