This report looks at changes in several key characteristics of the teaching force between the 1987-88 and 2011-12 school years, including the number of teachers, the level of teaching experience, and the racial/ethnic diversity of the teaching force. The report focuses on how these demographic changes varied across different types of teachers and schools.

Among the findings about changes in the teacher workforce over this 25 year period:

• The teacher work force grew by 46 percent between 1987-88 and 2011-12. Above average growth was seen among teachers in the fields of English as a Second Language, English language arts, mathematics, foreign language, natural science, and special education. Below-average growth was seen in the fields of general elementary education, vocational-technical education, and art/music;


• The growth in the teaching force varied across different types of schools. The teaching force in high-poverty public schools grew by nearly 325 percent while the number of teachers in low-poverty schools declined by almost 20 percent. The number of teachers in private schools grew at a higher rate than in public schools. However, private school teachers still account for only about 12 percent of the teacher work force; and


• The teacher force became more diverse. While minority teachers remain underrepresented in the teaching force, both the number and proportion of minority teachers increased. Between 1987–88 and 2011–12, the number of minority teachers grew by 104 percent, compared to 38 percent growth in the number of White teachers. The percentage of teachers who belonged to all minority groups increased from 12.4 percent in 1987-88 to 17.3 percent in 2011-12.

This report utilizes data from the Schools and Staffing Survey (SASS), a large-scale sample survey of elementary and secondary teachers and schools in the United States. SASS has been conducted seven times—in school years 1987-88, 1990-91, 1993-94, 1999-2000, 2003-04, 2007-08, and 2011-12.

In some tests of educational interventions, individual students are randomized directly to the treatment or control group, and both intervention and control protocols are administered in an individual setting. Such an experiment is an Individual-Level Randomized Controlled Trial (I-RCT). In other tests, clusters of students (e.g., classrooms) are randomized. This sort of experiment is called a Cluster Randomized Controlled Trial (C-RCT). However, in some designs, students in the treatment group are clustered like those in a C-RCT, but students in the control group are unclustered, like students in an I-RCT. This design is called a Partially Nested Randomized Controlled Trial (PN-RCT). It is partially nested because students in the treatment group are nested in some higher level unit, such as a tutoring group or class, but students in the control group are not nested as part of the experimental design.

This paper, commissioned by the National Center for Education Research, provides readers with an introduction to PN-RCTs and ways to design and analyze the results from them. This paper was written primarily for applied education researchers with introductory knowledge of quantitative impact evaluation methods. However, those with more advanced knowledge will also benefit from some of the technical examples and appendices.

• Chapters 1 and 2 define PN-RCTs and address design issues such as possibilities for random assignment, cluster formation, statistical power, and confounding factors that may mask the contribution of the intervention.
• Chapter 3 discusses basic statistical models that adjust for the clustering of treatment students within intervention clusters, associated computer code for estimation, and a step-by-step guide, using examples, on how to estimate the models and interpret the output.
• Chapter 4 and the technical appendixes discuss more advanced statistical topics pertaining to PN-RCTs.

• Assessment: What have we learned about effective identification and assessment of students who have or are at risk for reading difficulties or disabilities?
• Basic Cognitive and Linguistic Processes: What are the basic cognitive and linguistic processes that support successful reading and how can these skills be improved for students who have or who are at risk for reading disabilities?
• Intervention: How do we make reading instruction more effective for students who have or are at risk for developing reading disabilities? How do we teach reading to students with low incidence disabilities?
• Professional Development: How do we bring research-based instructional practices to the classroom?