Dual-language immersion programs--in which students learn core subjects (language arts, math, science, and social studies) in both English and a "partner" language--have been gaining in popularity across the United States. Such programs may use a "two-way model," in which roughly half the students are native speakers of the partner language and the other half are native speakers of English, or a "one-way model," in which most students are native speakers of a single language. The growing demand for these programs is due in part to studies that have linked dual-language immersion to academic and cognitive benefits for students, regardless of their native language or socioeconomic status. Based on these findings, many educators and policymakers see dual-language immersion, and particularly two-way programs, as a promising way to close achievement gaps and foster academic success for English learners and other disadvantaged students. The Portland Public School District in Oregon has offered dual-language immersion programs since 1986. To understand how such programs are implemented in classrooms, the Research and Development (RAND) Corporation and the American Councils for International Education partnered with the district to observe teachers and students in a subset of Portland's two-way and one-way immersion classrooms. The observations were undertaken as part of a four-year study funded by the U.S. Department of Education's Institute of Education Sciences to assess the causal impact of dual-language immersion programs on students' academic achievement. The observation data discussed in this research brief were collected from the district's two-way programs in Spanish and Russian in spring 2013 and spring 2014. Data collection focused on two important aspects of fidelity of implementation: the extent to which teachers used the instructional practices recommended by the district (i.e., "quality of delivery") and the extent to which teachers and students spoke or wrote in the partner language during class periods designed to be conducted in that language (i.e., "adherence to the model"). This research brief summarizes key findings from the observation data and offers a descriptive view of classroom practices in two-way programs in the district. Key findings include: (1) Teachers in two-way dual-language immersion classrooms consistently implemented key instructional practices targeted by the school district. Key findings include: (2) Teachers strongly adhered to guidelines about language use: For classes that were supposed to be taught in a partner language, teachers stayed in the partner language for the entire period in 57 percent of the observed classes; in 40 percent of the observed classes, they did so for almost the entire period; and (3) Students were less consistent in their language use during partner language lesson activities: Students fully adhered to the partner language while speaking to teachers in 27 percent of the observed class periods; they did so while speaking to peers in only 20 percent of the observed class periods. [This brief describes work done in RAND Education and documented in "Teaching Practices and Language Use in Two-Way Dual Language Immersion Programs in a Large Public School District," "International Multilingual Research Journal," Vol. 10, No. 1, January 2016, pp. 31-43. For this article, see EJ1088159.]