Feb. 10 (Bloomberg) — When Robin McLane's generation hit public schools in the 1950s, there were never enough classrooms or teachers to accommodate the bulge, she said. So she's not surprised about the latest shock that boomers are delivering to the U.S. economy.

"People all around me, relatives and friends, are either retiring, or they're finding it's very difficult to find work anywhere from 55 on," said the 65-year-old, who lives in Portsmouth, New Hampshire, and retired from her job as a high school literacy specialist in June. "For me, I was ready to move on."

The share of Americans in the labor force, known as the participation rate, is hovering around an almost four-decade low as the population ages and discouraged job seekers give up looking for work. Federal Reserve research shows retirees are at the forefront of the recent exodus, which blunts the impact of policy aimed at boosting the economy and workforce.