The majority of tests used in the current U.S. school system focus mainly on achievement of content knowledge and rely heavily on multiple-choice items, measuring primarily low-level knowledge and some basic skills.[24] A study by the RAND Corporation found that, in the 17 states studied, fewer than 2% of mathematics items and only about 20% of English language arts (ELA) items on state tests ask students to analyze, synthesize, compare, critique, investigate, prove, or explain their ideas.[24]