In the world's richest countries, some children do worse at school than others because of circumstances beyond their control, such as where they were born, the language they speak or their parents' occupations. These children enter the education system at a disadvantage and can drop further behind if educational policies and practices reinforce,…

Whether in health, in education, or in material well-being, some children will always fall behind the average. The critical question is -- how far behind? Is there a point beyond which falling behind is not inevitable but policy susceptible, not unavoidable but unacceptable, not inequality but inequity? There are no widely agreed theoretical…