The Common Core State Standards in Mathematics (CCSS-M) were released in 2010 with a goal to improve critical thinking skills and prepare all students to thrive in college, careers, and as informed citizens. The Next Generation Science Standards (NGSS) followed in 2013. Using districtwide surveys of students in grades 6-8, conducted annually from 2011 through 2018; annual data on student achievement; surveys of teachers in the 2014-15 and 2017-18 school years; and interviews of teacher-leaders, school principals, and district officials, this study examines the results of district efforts to implement the CCSS-M and NGSS standards in Chicago. Findings include: (1) Math and science instruction improved in Chicago during the years of standards reform. In math, the largest improvements in instructional experiences and test gains occurred among students with the lowest tested skills; (2) Professional learning--defined broadly to include teacher collaboration, coaching, and workshops--was the most support that was most strongly associated with instructional change; (3) Collaboration around instructional improvement required dedicated time, multiple people with expertise, buy-in, trust, and administrator support; (4) Instructional resources provided by the district were helpful for implementing strong practices when they were instruction-ready, while other resources showed a null or negative relationship with practices; and (5) Instructional practices were significantly related to student achievement gains in both math and science. [This report was written with Jeanne Century, Debbie Leslie, Lisa Sall, and Nick Tallant.]