Standards-based reform (SBR) has been an important policy in U.S. K-12 education for at least the last 25 years. The theory of change for SBR suggests that, with coherent content standards in core academic subjects, measurable goals for student learning, and appropriate supports and accountability measures, teachers will modify their instruction to align with standards and assessments, and student learning will improve. While many studies have evaluated the effects of SBR on achievement, few have addressed the content of instruction, the primary means by which SBR is intended to have its effects. The few studies of instruction have focused mainly on pedagogy, or they have suffered from serious methodological and substantive problems that bring into question the validity of their findings. The purpose of this dissertation is to address this gap in the literature by using survey data on the content of teachers’ instruction in mathematics, science, and English language arts and reading (ELAR) to investigate changes in a) alignment to standards and assessments, b) hours of instruction, and c) emphasis on various levels of cognitive demand (e.g., memorizing, procedures) in the years 2003-2009. In addition, attributes of the standards-based accountability system are studied for their relationship with instructional alignment. The methods used include fixed-effects models and three-level hierarchical linear modeling. The results suggest that alignment to standards and assessments in mathematics increased during the years 2003-2009 by approximately .3 to .5 standard deviations. Alignment also increased to science standards at grades 3-8, but there were no consistent changes in alignment in ELAR or at other grades. Shifts of instructional time were small and generally non-significant. Teachers were found to increase their focus on lower-level thinking (e.g., procedure, memorization) in most grades and all three subjects. Generally, these shifts brought teachers’ instruction into greater agreement with standards and assessments. Finally, alignment was higher when standards and assessments were well aligned with each other (average standardized effect size = .22σ), when the standards were broad and focused on many ideas (.50σ), and when the state had stronger policies emphasizing rewards and sanctions (.12σ). Implications for policy and research are discussed.