Labor productivity expanded at twice the rate expected in the second quarter, accelerating from the start of the year. That was an acceleration in productivity growth from the first quarter. The first quarter’s growth rate was revised up to 0.8 percent from the preliminary estimate of 0.3 percent. Rising productivity is regarded by many economists as the key to noninflationary economic growth. In a period in which the workforce is growing slowly, thanks to falling fertility among U.S. residents two decades ago that continues today and stricter enforcement of immigration laws, productivity growth is likely to be the main driver of economic growth.