Graduate teaching assistants at the University of Michigan at Ann Arbor staged a 12-hour strike Thursday in the hopes of disrupting the campus and pressuring administrators into concessions at the bargaining table. Amid the usual disputes over numbers of protesters and canceled classes, leaders of the Graduate Employees Organization described the day as a “success,” while a Michigan spokeswoman said the strike had resulted mostly in “inconveniences.”

Dave Dobbie, president of the Graduate Employees Organization and a doctoral student in social work and sociology, said the union had largely achieved its goal of “shutting down the campus.”

While acknowledging that he did not have “any quantitative measures,” he said that it “seems pretty clear that a majority of classes on the campus” were called off. He said that many adjunct instructors had canceled their classes in solidarity and that scores of construction workers on the campus had forfeited a day’s pay to join the picket lines.

And speaking by cell phone as he stood in a central campus spot, Dobbie said that “where there are usually floods of students, there seem to be very few people going by.” He added: “The campus is dead today, and in that way, it’s a success.”

Julie Peterson, a spokeswoman for the university, offered a markedly different picture. She estimated the number of picketers at a “couple hundred,” and said a survey by Michigan administrators showed that “most of the schools and colleges were reporting little or no impact on their classes.”

She acknowledged, though, that a “handful of departments” in the College of Literature, Science, and the Arts, where about two-thirds of the 2,100 “graduate student instructors” work, were reporting the cancellation of a “large proportion” of their classes. The engineering school, the second-biggest employer of teaching assistants, had virtually no cancellations, Peterson said. “Over all, it’s spotty.”

Peterson also said the strike had had some impact on “business operations,” as the graduate students’ union set up picket lines on loading docks and at construction sites where they knew other union workers “will not cross picket lines.” Those efforts resulted in delays in deliveries and building construction that she describes as “inconveniences” with “no cost impact to the university.”

“It’s really just a matter of making up the work later,” she said.

At issue in the dispute are pay and benefits for the graduate instructors, who teach a little under a quarter of all undergraduate course sections. The university’s four-year contract with them expired in February, and they have been working without one since then. Negotiations began in November but the university and the union, an affiliate of the Michigan Federation of Teachers, remain far apart on several key issues, notably wages and health care benefits and costs. Graduate employees at Michigan now earn about $14,000 a year on average for what the university characterizes as about half-time work.

Dobbie said the union called the strike Wednesday night after it offered a compromise on wages and the university declined to make a counterproposal. The union, Dobbie said, had offered to cut their salary demands significantly -- from $16,000 a year next year and cost of living increases of 5 percent a year in the three years after that, to $15,300 next year and just cost of living adjustments in the three subsequent years.

On an administration Web site about the negotiations, university officials said the union proposal would amount to a 9 percent increase next year and a total boost of about 20 percent over the term of the contract. The university wants to continue to tie pay increases for graduate employees to those for faculty members in Michigan’s main undergraduate liberal-arts college, while guaranteeing a minimum increase of 2 percent the first year and 2.5 percent in the next three years.

The two sides are also far apart on health care issues. University officials say they’ve proposed significant expansions of current benefits, including adding dental insurance from day one and a $30,000 life insurance policy. Dobbie says the union wants Michigan to lock in health benefits and co-pay and other costs at their current levels through the term of the contract.

Dobbie said that the union’s ultimate hope in striking was that “through a demonstration of how much support we have on campus, and how unified our membership is, that the university will come back to the table [Friday] with more serious counterproposals.”

Said Peterson: “We'll go back to bargaining in the afternoon. Hopefully we'll make some progress.”