BOSTON — Changes are coming in standardized testing for many Massachusetts school districts.According to data from the Massachusetts Department of Elementary and Secondary Education, 54 percent of school districts have opted to administer the English and mathematics PARCC exams to students in grades 3-8 next year, instead of the MCAS exams.PARCC, short for Partnership for Assessment of Readiness for College and Careers, was developed as part of the national Common Core standards.