21st Century STEM for Girls and Underrepresented Minorities Act

21st Century STEM for Girls and Underrepresented Minorities Act - Amends the Elementary and Secondary Education Act of 1965 to authorize the Secretary of Education to provide grants to, and enter into agreements with, local educational agencies (LEAs) to improve the education of girls and underrepresented minorities in science, technology, engineering, and mathematics (STEM) and prepare them to pursue undergraduate and graduate degrees and careers in such fields.

Gives priority to LEAs that partner or coordinate with local, regional, or national entities experienced in increasing the participation of girls or underrepresented minorities in STEM.

Requires the use of grant funds to: (1) involve the parents of girls and underrepresented minorities in stoking their children's interest in STEM, (2) provide tutoring and mentoring programs in such fields, (3) expose girls and underrepresented minorities to STEM role models, (4) enable such students and their teachers to attend STEM events outside the classroom, (5) provide after-school and summer programs for students in such fields, (6) purchase education materials or equipment to facilitate STEM instruction, (7) provide such students with academic advice and assistance in selecting high school courses, (8) pay up to 50% of the cost of a STEM internship for such students, and (9) train school personnel to facilitate students' progress in such fields.