New Delhi, May 8 -- Tamil Nadu and Kerala are among India's most socially advanced states, with new governments ready to take charge. They are faced with a more complex challenge than many parts of the world that are still grappling with basic developmental deficits.

How do they maintain prosperity, create more economic resilience and generate the next wave of opportunity?

The numbers tell a powerful story. Tamil Nadu and Kerala have two different but relatively successful development models in the most prosperous part of the country-southern India.

Southern India accounts for almost 30% of India's household disposable income, while it has about 24% of its households. The region is also home to 28% of India's middle-class households, m...