Previous research demonstrates enhanced speech perception abilities for typically hearing and hearing-impaired listeners when speakers use clear versus plain speech, particularly in the presence of background noise. To date, very few studies have investigated the effects of noise on word learning and no studies have examined the effects of clear and plain speech on the ability to learn new vocabulary items in quiet or in the presence of background noise. This study examines the effects of noise (studies one and two) and speaking style (study two) on word learning in typically developing school-aged children (9;0 to 10;11 year olds) at both the fast and extended mapping stages of word learning. Participants in study 1 completed a novel word mapping task and a word recognition task in varying degrees of background noise. The purpose of study 1 was to examine how word recognition and mapping are affected by different degrees of cognitive load and varying degrees of background noise. Participants in study 2 completed an extended novel word learning task in either quiet or noisy conditions with both clear and plain speech. Study 2 directly examined the effects of speaking style on word learning abilities in quiet and noisy acoustic environments. Results of both studies demonstrate the detrimental effects of background noise on school-aged children's abilities to learn new lexical items. Specifically, we found that noise interferes with children's ability to hold newly heard lexical items within working memory as evidenced by significantly poorer performance on the mapping probe compared to performance on the recognition probe of study one. In our second study, we found that the participants who learned new words in the presence of background noise named significantly fewer items on a production probe than did the participants who learned words in a quiet environment despite equivalent comprehension probe performance. We found marginal improvements in word learning abilities when the target items were produced with a clear speaking style compared with a plain style. Theoretical and practical implications 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.]