Though the majority of the world’s population is bilingual, most of the existing research on child language acquisition has focused on monolinguals. Increasingly, research has begun to investigate language acquisition in bilingual contexts, and has found evidence of both similarity to and difference from patterns found in monolingual language acquisition. One evident source of difference in bilingual language acquisition is interaction, where bilinguals’ acquisition of one language affects their acquisition of the other language. Interaction has been shown to occur at multiple levels of linguistic structure (syntactic, phonological, phonetic), and manifests in three different patterns: acceleration, deceleration, and transfer. Acceleration and deceleration refer to the rate at which bilinguals acquire some property relative to monolinguals in the same language. Acceleration occurs when bilinguals acquire some property faster or earlier compared to monolingual peers, whereas deceleration occurs when bilinguals acquire some property later or more slowly than monolingual peers. Transfer refers to bilinguals’ use of a property specific to one language in their other language. While the occurrence of each of these patterns has been demonstrated in bilinguals’ language acquisition, it is not well understood what causes interaction to occur where and how it does. In this dissertation, I propose that frequency of occurrence and linguistic complexity, both features of the input that are known to affect the course of monolingual acquisition, also direct the appearance of interaction in bilinguals’ acquisition of language. I present findings from a series of studies demonstrating that differences between languages in frequency of occurrence and complexity of phonological properties influence bilinguals’ acquisition of aspects of Spanish and English phonotactics in predictable ways. Specifically, greater frequency of occurrence and greater complexity of phonological properties in one language are shown to promote bilinguals’ acquisition of related phonological properties in their other language.

Phonological disorder is a language impairment with no known cause that primarily affects the phonological domain. It is a highly prevalent and impactful communication disorder, yet it has a relatively stagnant history of standardized or relational assessment techniques and traditional, bottom-up remediation approaches designed, primarily, for monolingual speakers of majority varieties of English. Although assessment and treatment for phonological disorder is effective, traditional approaches are not optimized for maximizing efficient phonological growth, which may be achievable by incorporating knowledge of complex phonological structure into the target selection process. Further, the evidence base fails to address the diverse impairment profiles and language backgrounds of many children with phonological disorder. By drawing on our understanding of phonology, phonological analysis, and phonological development, we can work towards advancing efficient and equitable assessment and intervention approaches for a clinically and linguistically diverse population of children with phonological disorder.Chapter 1 provides an overview of the current state of intervention for phonological disorder, highlighting areas of need related to the efficiency and equity of clinical services for this population. Chapter 2 describes a new assessment tool, AutoPATT, and a study examining its validity and accuracy for generating independent, descriptive phonological assessment measures. Chapter 3 investigates the relationship between phonemic inventories generated by AutoPATT and more traditional accuracy measures by comparing both measures derived from single-word productions of 275 English-speaking children with phonological disorder. Chapter 4 examines the phonological influences affecting explicit marking of English tense and agreement morphemes in the connected speech of typically developing Spanish-English bilingual children. Chapter 5 presents a case study exploring the use of a word-final treatment target containing complex phonological and morphological components to remediate co-occurring phonological and morphosyntactic deficits. Chapter 6 is a study comparing the efficacy and efficiency of treatment with complex consonant clusters and singleton targets in Spanish for Spanish-English bilingual children with phonological disorder. Chapter 7 concludes with a general discussion of the findings from these studies and describes pathways for continued work to advance the efficiency and equity of assessment and treatment for phonological disorder.