Parents want to provide the best environment for their child, but delaying school is rarely the right approach. The first six years of life are a time of tremendous growth and change in the developing brain. Synapses, the connections between brain cells, are undergoing major reorganization. Indeed, a 4-year-old’s brain uses more energy than it ever will again. Brain development cannot be put on pause, so the critical question is how to provide the best possible context to support it.

For most children, that context is the classroom. Disadvantaged children have the most to lose from delayed access to school. For low-income children, every month of additional schooling closes one-tenth of the gap between them and more advantaged students. Even without redshirting, a national trend is afoot to move back the cutoff birthdays for the start of school. Since the early 1970s, the date has shifted by an average of six weeks, to about Oct. 14 from about Nov. 25. This has the effect of making children who would have been the youngest in one grade the oldest in the next-lower grade; it hurts children from low-income families the most.