Undercover Economist gets to the bottomline

"Still, one thing is certain: since your boy has a mother who is fussing about this sort of stuff, he’s going to do fine no matter what."

That in answer to this question: "My four-year-old son has a July birthday, which would make him one of the youngest in his class at school. I am thinking of keeping him back a year so that when he does start school, he’ll be bigger and more confident. Is this a good idea?"

In a related vein, see James Heckman's essay, The Growing Polarization of American Society and it Implications for Productivity, at VOX. An extract:

Fifty percent of the variance in inequality in lifetime earnings is determined by age 18 (Cunha and Heckman, 2007). The family plays a powerful role in shaping adult outcomes that is not fully recognised by current American policies. As programs are currently configured, interventions early in the lives of disadvantaged children have substantially higher economic returns than later interventions such as reduced pupil-teacher ratios, public job training programs, convict rehabilitation programs, adult literacy programs, tuition subsidies, or expenditure on police. This is because life-cycle skill formation is dynamic in nature. Skill begets skill; motivation begets motivation. Motivation cross-fosters skill, and skill cross-fosters motivation. If a child is not motivated to learn and engage early on in life, the more likely it is that when the child becomes an adult, he or she will fail in social and economic life.

Read it all, it's good throughout.