Public pensions had median increases of 16.9 percent for the 12 months ended June 30, according to data from the Santa Monica, California-based consulting firm. It was the best performance since the funds rose 21.2 percent in fiscal 2011. Those with assets greater than $1 billion performed best, reporting median jumps of 17.4 percent, boosted by bigger allocations to private equity, hedge funds and other alternative assets.

Smaller state and local-government pensions target more of their money to less-risky U.S. bonds, which hindered their performance relative to larger plans, said Robert Waid, a managing director at Wilshire.

"Alternatives outperformed the non-U.S. equity asset class," Waid said in a telephone interview. "Larger public plans are more likely to have more exposure to alternatives."