Stock-fund managers are off to a great start this year. Of diversified large-stock funds, Morningstar Inc. indicates 64% beat the Standard & Poor’s 500-stock index in the first two months of 2012, as opposed to 20% in 2011. Aaron Reynolds, associate director of asset-manager research at Milwaukee-based securities firm Robert W. Baird & Co. contends the sudden performance-enhancement has more to do with the cyclical pattern of managers beating a benchmark than anything the managers are doing. “Managers are adaptive, but they don’t change their stripes all that often,” says Mr. Reynolds. John Cochrane, a finance professor at the University of Chicago Booth School of Business, delivered another ego-blow to managers: investors can assemble their own portfolio of exchange-traded funds with the same market exposure, which raises the question of a manager’s value.