Strength in Diversity Act This bill amends the Elementary and Secondary Education Act of 1965 to establish the Strength in Diversity Program, through which the Department of Education (ED) shall award competitive grants for the development or implementation of plans to improve diversity or eliminate socioeconomic or racial isolation in public schools and publicly funded early education programs. The grants are available to local educational agencies, a consortium of such agencies, educational service agencies, or other regional educational authorities that have significant achievement gaps and socioeconomic or racial segregation within or across the school districts served by the entity. ED may give priority to an eligible entity that proposes to use funds to support a program that extends beyond one local educational agency. Each recipient of an implementation grant shall implement a high-quality plan that includes: a comprehensive set of strategies designed to improve academic outcomes by increasing diversity, evidence of strong family and community support for these strategies, ambitious but achievable goals to increase diversity over the grant period, collection and analysis of data to provide transparency and support continuous improvement throughout the grant period, and a rigorous evaluation of the proposed project's effectiveness. ED shall establish performance measures to track the progress of each grant recipient.