Providing Resources and Organization to Maximize Opportunities for Training and Education in STEM Act of 2020 or the PROMOTES Act of 2020 This bill authorizes the Department of Defense (DOD) to carry out a grant program to assist high schools in providing education to students in the Junior Reserve Officers' Training Corps in subjects including science, technology, math, engineering, computer science, and related areas. Local educational agencies may use grant funds for purposes including training and other support for instructors, acquisition of instructional materials, travel opportunities, mentoring programs, and certifications for students. In making the grants, DOD must give preference to schools with high percentages of children from low-income families.