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Lexical acquisition, involving development of vocabulary and related conceptual knowledge, is a cognitively demanding task that provides a substantial challenge for children. Young children's oral vocabulary and conceptual knowledge development are critical for lifelong success with all aspects of literacy, including oral and written communication as well as listening and reading comprehension. This development process involves children's gradual appropriation of semantic knowledge through interactions with more proficient speakers. Through the acquisition of knowledge about words, relations between words, and underlying conceptual understanding, children develop increasingly strong and diversified word-referent relationships. At the inception of formal schooling, young children have experienced profoundly diverse language and literacy experiences. Such discrepancies yield substantial variation in children's linguistic repertoires, particularly with respect to oral vocabulary and conceptual knowledge, a phenomenon referred to as the "vocabulary gap" which may grow exponentially over time. A growing lexical deficit may be masked by children's early success with foundational literacy skills including phonemic awareness, the alphabetic principle, decoding, and fluency. Given its placement as the introduction to formal schooling, the kindergarten year may constitute the preeminent time for incorporation of focused instruction in vocabulary and conceptual knowledge to help mitigate this gap. A collection of instructional features -- small group instruction, repetition of words and content, and reading text aloud to students -- has shown consistent benefits for development of oral vocabulary and conceptual knowledge. Successful acquisition of new lexical knowledge is also contingent upon participation in contexts with dialogue that enables children to make semantic inferences. Three diverse pedagogical styles used in text-based dialogue -- 1) Teacher-directed instruction, 2) Jointly constructed teacher and student instruction, and 3) Student-driven instruction -- have each shown benefits for young learners' development of oral vocabulary and conceptual knowledge. Variation in the genre of text used within this dialogue may offer unique benefits to young children's oral vocabulary and conceptual knowledge development. However, instructional practices that most effectively contribute to early mitigation of the disparities in oral vocabulary and conceptual knowledge have not yet been identified in a comprehensive manner. The research study undertaken in this dissertation is intended to shed light on these instructional practices by addressing the following research question: How do discussions during teacher read-alouds foster kindergarteners' oral vocabulary and conceptual knowledge development? Three sub questions based on the primary independent variables were established: 1) How does variation of instructional style affect kindergarteners' oral vocabulary and conceptual knowledge development? 2) How does variation of text genre affect kindergarteners' oral vocabulary and conceptual knowledge development? 3) How do instructional style and text genre interact to affect kindergarteners' oral vocabulary and conceptual knowledge development? The central component of the study involved an experimental instructional intervention consisting of a series of small-group read-aloud discussions. Administration of the intervention was a between-subjects factor, with experimental group participants receiving the intervention and control group participants not receiving the intervention. The intervention with the experimental group was a within-subjects factor, with each experimental subgroup participating in every level of the independent variable. Three instructional units, each centered on one focal narrative text and one focal informational text, were implemented in the intervention. Prior to the intervention, a pair of texts was selected as the focus for each unit. Eight focal vocabulary words were selected from each text. Texts and vocabulary words were subject to a battery of criteria before inclusion in the intervention. Two norm-referenced vocabulary assessments, the PPVT and the EVT, were administered to all participants at the beginning and end of the intervention. A series of researcher-designed vocabulary and conceptual knowledge assessments, based on the focal words and content of the focal texts, was administered to all participants at the beginning and end of each instructional unit. Specific instructional protocols were also established to ensure teacher fidelity to the focal instructional style for each discussion. The study consisted of a 3 x 2 x 2 x 2 mixed-subjects fractional factorial design. The first primary independent variable, Instructional Style, referred to the nature of the discussion format taking place in the small group read-aloud sessions, and was comprised of three-levels: Teacher-Driven, Joint-Teacher-Student-Driven, and Student-Driven. The second primary independent variable, Text Genre, referred to the type of text that was the focus of the small group read-aloud sessions, and was comprised of two levels: Narrative and Informational. The first secondary independent variable, Word Focus, referred to the instructional attention placed on the vocabulary words measured in the specific vocabulary assessments, and was comprised of two levels: Target and Non-Target. The second secondary independent variable, Text Sequence, referred to the order in which the texts were presented within the instructional unit, and was comprised of two levels: Narrative followed by Informational and Informational followed by Narrative. The study was conducted at a full-inclusion Title I kindergarten through Grade 8 suburban public elementary and middle school in Northern California. The majority of the students at the school were from low SES households. 49 students (21 males, 28 females), with an average age of 5.42 years at the beginning of data collection, participated in the duration of the study. The racial/ethnic composition of the sample was 63% Latino, 18% Pacific Islander, 14% African-American, and 4% multiple ethnicities. Employing a randomized block design, participants' language scores on the norm-referenced PPVT and EVT assessments were used to assign them heterogeneously to one of six experimental groups or to the control group. Each experimental group consisted of six students, for a total of 36 students in the experimental condition and 13 students in the control condition. Quantitative data analysis consisted of a series of analyses of variance (ANOVA) to identify potential main effects of each independent variable and potential interactions among the independent variables. Qualitative analysis consisted of establishment of unique coding frameworks for oral vocabulary and conceptual knowledge based on patterns of teacher and student utterances that surfaced in the small-group read-aloud discussions. The experimental groups tended to show more growth than the control group on both norm-referenced measures of vocabulary knowledge, all measures of specific vocabulary knowledge, and both measures of conceptual knowledge. These differences in performance suggest that kindergarten students' participation in small-group text-based discussions may contribute to growth in oral vocabulary and conceptual knowledge beyond the growth that takes place during the course of the kindergarten academic year in the absence of this instructional intervention. On all measures of specific vocabulary knowledge, students showed greater performance on target word knowledge relative to non-target word knowledge. These differences suggest that attention to and discussion of vocabulary, in addition to hearing the words read aloud in text, may be an essential practice for promoting vocabulary growth. Students demonstrated measurable oral vocabulary and conceptual knowledge growth following participation in text-based discussions adhering to each of the three instructional styles. However, students tended to show the greatest growth in both oral vocabulary and conceptual knowledge following participation in text-based discussions adhering to a Teacher-Driven instructional style. The highly structured nature of these sessions, in conjunction with student participation in the form of prompted repetition and demonstration, as well as exclusive use of examples by students, may be associated with the observed greater performance in vocabulary and conceptual knowledge following the Teacher-Driven sessions. Students showed measurable oral vocabulary growth following participation in text-based discussions based on both narrative and informational texts. However, students tended to show the greatest vocabulary growth following participation in text-based discussions focused on narrative texts. Discussions for the narrative genre featured greater use of focal words, nonverbal support, and prompted demonstrations, as well as exclusive use of examples and categorization of words, each of which may be associated with the observed increase in vocabulary performance relative to that following discussions of informational text. While the design of the current study prohibited a direct comparison of conceptual knowledge growth according to text genre, the nature of the texts and student performance suggest that informational texts may have been most beneficial for conceptual knowledge growth. Discussions in the informational genre included exclusive use of teacher examples and nonverbal support, as well as exclusive student use of questions and nonverbal support, each of which may be associated with conceptual knowledge performance following discussions of informational text. Additionally, informational texts offered more explicit access to conceptual knowledge via text and photographs. This more dir ...
