From The New York Times: It was once common for elementary-school teachers to arrange their classrooms by ability, placing the highest-achieving students in one cluster, the lowest in another. But ability grouping and its close cousin, tracking, in which children take different classes based on their proficiency levels, fell out of favor in the late 1980s and the 1990s as critics charged that they perpetuated inequality by trapping poor and minority students in low-level groups. Now ability grouping has re-emerged in classrooms all over the country – a trend that has surprised education experts who believed the outcry had all but ended its use.