Complex sentence: Most students score highly on standardized tests (the AP, the SAT, the PSAT/NMSQT, the High School Proficiency Assessment-HSPA), as well as performing well in competitions such as the American Mathematics Contest or the Science League.
Split into simpler sentences: Most students score very highly on standardized tests (the AP, the SAT, the PSAT/NMSQT, the High School Proficiency Assessment-HSPA). They also perform well in competitions such as the American Mathematics Contest or the Science League.