Domain-specific vocabulary knowledge is an important precursor to overall knowledge acquisition, which is essential to reading and comprehending grade-level texts. There are a number of malleable factors within the classroom that can be shaped by teachers and policy makers, yet additional empirical evidence is needed to uncover and evaluate those factors. In the following dissertation papers, I propose a series of studies that are interconnected and closely examine vocabulary development and acquisition. Each study aims to identify specific factors and mechanisms within the classroom that can be enhanced through intervention research. In my first study, I use a mixed-methods design with confirmatory and exploratory aims. For the confirmatory portion, I leverage a large randomized controlled trial to test a conceptual model that examines whether and to what extent the effects of a two-year first- and second-grade content literacy intervention are mediated via the acquisition of domain-specific vocabulary knowledge over first and second grades. For the exploratory portion of the study, I use survey data and semi-structured interviews of 48 second-grade teachers to expand upon the quantitative findings to gain greater insight into the vocabulary practices of treatment and control teachers. In the second study, I extend the findings from study 1 by designing an intervention that explores how "structured supplements" for a read aloud lesson can promote transfer in reading comprehension on measures of recall, near-transfer, and mid-transfer. Structured supplements can enhance a read aloud lesson by including concise and meaningful definitions and examples of word meanings, highlighting conceptual connections between words, engaging discussion prompts that get students talking about topics with key vocabulary, and an activity helping students see connections between known and new topics. In my final study, I expand upon an existing measure of teachers' knowledge of teaching vocabulary by adding additional items that focus on teaching domain-specific vocabulary and morphology. I use Item Response Theory (IRT) to examine the psychometric properties of the items and multilevel structural equation modeling (MSEM) to see if and to what extent the revised measure of teachers' knowledge of teaching vocabulary correlates with student outcomes. Combined, the three studies within this dissertation contribute to the field's understanding of the role domain-specific vocabulary instruction plays in reading comprehension through descriptive, causal, and process evidence. Targeted shifts in instruction have the potential to improve educational outcomes for all students and these three studies contribute to understanding how the field can better support teachers and students. [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.bibliotheek.ehb.be/en-US/products/dissertations/individuals.shtml.]