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The largest in a series of rolling sickouts by teachers protesting the conditions of Detroit schools nearly shut down the entire district Wednesday, just as President Obama was expected to arrive in town.

All but a dozen or so of the city's 100 public schools were closed Wednesday, forcing most of the district's 46,000 students to stay home, according to local NBC affiliate WDIV.

Many of the teachers rallied outside the Cobo Center, where Obama was scheduled to speak to a United Auto Workers gathering.

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Detroit teachers have been staging sickouts — the organized but unauthorized taking of sick days — to draw attention to the district's financial straits and crumbling buildings and to express their opposition to Gov. Rick Snyder's public education policies.

The centerpiece of Snyder's plan to turn the system around is a 10-year, $715 million refinancing scheme that would split the district — already run by an emergency manager he appointed — into two as a way to pay off crippling debts.

Many teachers say the plan threatens to undermine the public school system and disenfranchises city residents.

Teachers from Detroit area schools protest outside Cobo Center before President Barack Obama's visit to the auto show on Jan. 20. Todd McInturf / Detroit News via AP

Wednesday's sickout was the biggest in a string of similar actions in recent weeks, reportedly organized by a group affiliated with the teachers union called DPS Teachers Fight Back. More than 60 schools were forced to close Jan. 11.

The sickouts have not risen to the level of an all-out strike, because such a move is prohibited by Michigan law.