The California Public Employees’ Retirement System, the largest U.S. pension at $252.3 billion, earned about 13 percent on invested assets last year, led by increases in stocks and private equity.

That compared with a 1.1 percent return in 2011, according to the fund. Private-equity investments, whose reporting lags behind the rest of the results, climbed about 12 percent for the year through September, less than half the target rate, Calpers said yesterday. Publicly traded shares rose about 17 percent, meeting goals for the period ending Dec. 31.

Public pensions such as Calpers have been under pressure to boost investment returns following historic declines stemming from the global financial crisis and the 18-month recession that ended in 2009. In 2008, the Sacramento, California-based system lost almost 28 percent on investments.

“In pension-fund time, one year isn’t a long time,” Chief Investment Officer Joe Dear said at a Calpers board meeting in Monterey. “I’m pleased, but not excessively so.”

The fund has about 74 percent of assets required to meet long-term obligations, according to Calpers. When the pension’s investments underperform benchmarks, the state and municipalities must make up the difference.

For the first half of fiscal 2013, invested assets rose 7.1 percent. That’s an improvement from fiscal 2012, which ended June 30, when it earned just 0.1 percent. It was the third year in five that Calpers failed to reach the 7.5 percent threshold needed to meet projected obligations, data show.

For fiscal 2011, the system’s assets earned almost 21 percent, the best result since at least 1990, led by gains in stocks and private equity.

Following the historic declines, the fund set about restructuring its real-estate holdings, inserting more risk controls into investment decision-making, hedging some holdings against inflation, and allowing managers to better coordinate between asset classes.

Still, with half its assets invested in stocks, the fund is subject to market volatility. Its 10-year return as of Dec. 31 was about 7.5 percent.