Our three year old is in school simply because he’s ready to be there (wants to learn), but worry that as the years go by he might be at a disadvantage by being younger than his peers.  This is interesting and timely:

The less mature students, on the other hand, experienced positive effects from being in a relatively more mature environment: in striving to catch up with their peers, they ended up surpassing them.

via Against Redshirting: Why It Pays to Be the Youngest Kid in Class : The New Yorker.