STEM K to Career Act This bill amends the Higher Education Act of 1965 (HEA) to require the Department of Education to forgive student loan obligations of borrowers employed as full-time teachers of science, technology, engineering, or mathematics (STEM) in elementary or secondary schools in which the number of low-income children exceeds a certain percentage. Portions of the student loan debt, including interest, shall be forgiven on the basis of years of service, with 100% forgiven for five years of teacher service. The bill amends the Internal Revenue Code to allow: (1) an increased tax deduction for expenses by elementary and secondary school teachers for STEM education supplies; (2) a tax credit for the employment of STEM interns; and (3) a tax credit for employment of individuals who participated in an apprenticeship program in a STEM field, with the amount determined according to the degree of completion of a program. Beginning with FY2019, an institution of higher education must use at least 7% of federal work-study funds granted under the HEA to compensate students employed in STEM fields.