Big ideas are few and far between. Progress usually occurs incrementally, bit by bit. But sometimes a big idea – even one that starts modestly – can thoroughly transform our view of what is possible.

Last week, a small social experiment conceived 10 years ago to help 2,000 young delinquents in Peterborough, in eastern England, paid off – literally. More important, the Peterborough experiment has become the guiding light for hundreds of millions of dollars in investment in social reform.