to a test that it takes the joy out of teaching and learning. >> reporter: the mea culpa was timed to a survey released saturday showing standardized tests have exploded in the past decade. a typical american student takes 112 mandated standardized tests between pre-k and 12th grade. most countries that outperform the u.s. on exams test three times during their school careers. the debate stems from president george w. bush's no child left behind law and intensified last spring with new common core tests. opt-out movements have spread across the country amid growing concerns that tests are taking up too much classroom and time and leaving children over-stressed. teachers' groupch groups welcomed the changes. national education association president lily eskelsen garcia. >> we're quite pleased that at least they've taken one small step for childrenkind that says,