Strength in Diversity Act of 2020 This bill directs the Department of Education (ED) to award grants to specified educational agencies (e.g., local educational agencies) to develop or implement plans to improve diversity and reduce or eliminate racial or socioeconomic isolation in publicly funded early childhood education programs, public elementary schools, or public secondary schools. Specifically, ED may award planning and implementation grants to specified educational agencies. A recipient of a planning grant must use the grant to support students through certain activities, such as developing options to improve diversity in schools (e.g., weighted lotteries or school boundary redesign). Further, a recipient of an implementation grant must implement a high-quality plan to support students. This plan must, among other things, include a comprehensive set of strategies that are designed to improve academic outcomes for all students, particularly students of color and low-income students. A grant recipient may also use the grant for certain activities, such as recruiting additional teachers and staff, investing in specialized academic programs, and developing innovative and equitable school assignment plans. Additionally, ED may carry out national activities under the grant program, such as developing best practices for grant recipients and other experts in school diversity. The bill also requires ED to establish performance measures for the program and its related activities.