As soon as I walked into Celia Rojas’s prekindergarten class in Union City, N.J., I was sucked in by the hum of activity. Art plastered the walls, plants were hanging from the ceiling, and in every nook there was something to seize a child’s imagination. Some kids were doing cutouts of paper clothing and others were at an easel, painting. A bunch of children were solving puzzles on a computer, while another group was building a pink cardboard chair, which they called “A Chair for My Mother.” In the reading nook a girl was learning about how, when the wasp larva hatches, it eats the spider. Three classmates were playing dress-up, trying on old felt hats and checking themselves out in the mirror.