"A broad curriculum and assessment regime cannot exist alongside simple measurement, as it assumes a range of legitimate perspectives on knowledge, understanding and skills. Wider definitions of the curriculum are not easily measured and compared to allow sorting of students into winners and losers. in summary, the higher the stakes, the more relentless the focus on the target. Testing in turn assumes a simpler form (with exams being exalted as the only truly rigorous assessment) and the curriculum necessarily narrows. What matters is what is measured."
Stevenson, H., & Wood, P. (2014). Markets, managerialism and teachers’ work: the invisible hand of high stakes testing in England. International Education Journal: Comparative Perspectives, 12(2).