Number words and their written forms transform our quantitative reasoning as they are introduced into our cognitive experience by our parents, peers and school teachers.

He's talking about a cognitive limitation, "an important and pervasive problem in human reasoning" that he has documented by testing graduate students at the MIT Sloan School of Management.

Improving the health of school-going adolescents increases their enrolment and retention in school, their cognitive achievements, and leads to greater productivity.