King Banaian has a superb analysis of what happens in j-skools and in most newspapers in his explanation of why so many syndicated columnists (e.g. George Will) are conservative:
Suppose you run a paper that runs five op/ed columns a day. Four will be written by liberal commentators, one by conservatives in the interest of "balance". The market for liberal commentators flourishes and the j-schools flood with young liberals seeking entry into that market. The j-schools discourage conservatives from applying for admission, and as a result the market for conservative commentary contracts into a small oligopoly of a few writers. Each oligopolist is syndicated broadly; many of the liberal writers end up being columnists for a major city newspaper and not syndicated. Editors will eventually not carry local conservative writers, because a few columnists can dominate the industry and provide the conservative view at low cost. They, in short, outsource the right side of their "balanced" newspapers.
Then some guy gets the bright idea to test for media bias and chooses, as his measure, the number of papers each columnist appears in. What will he find?
What he finds is a great trove of small cottage liberal writing industry, and a few grizzled veterans of conservative commentary providing one column placed on the far side of hundreds of papers. And will report it as a success ... for conservatives.
And the newspapers will smugly report same, and the j-schools will tut-tut and go back to admitting [even] more liberals.