Friday is marked down as the "big push day" for Minneapolis teacher contract negotiations, after four months of talks that intensified this week.

Two notable overarching themes have emerged in discussions this week and previously.

First, the Minneapolis Federation of Teachers has put forward a proposal that asks no increase in the salary scales, except for beginning teachers. But that's based on its position that the district should absorb higher costs expected for some fringe benefits, such as family medical insurance premiums and pension contributions.

Second, much of the bargaining has centered on the district's push for contract changes it argues will achieve its goal of improving student performance at its worst-performing schools. It unveiled last month a laundry list of changes it wants at these 20 schools that the district defines as requiring major intervention.

The district is offering class-size targets that are four students lower per classroom than current staffing targets at these schools. That's one carrot. Another is that in exchange for a multi-year commitment by teachers to these schools, perhaps three years, the district would offer teachers there more protection from layoffs or getting bumped from their positions by more senior teachers.

But so far the union has said that granting layoff protection to these schools would mean the burden of absorbing layoffs falls more on remaining schools. It wants even lower class sizes and wants them guaranteed. It wants an out from the district's proposed three-year teacher commitment to allow a teacher to leave if a school isn't a good fit or for family or other needs.

The district also wants to use an expanded interview-and-select method to fill all vacancies at these schools, further modifying forced placement of more senior teachers. The union argues that seniority isn't the problem for low-performing schools but rather district-caused changes caused by closing schools or shifting programs.

The district wants to require teachers at these schools to participate in another five weeks of training in the summer, later reduced to three weeks. But a key issue has been whether they'll get full pay or the lower staff-development pay rate. The union raised questions about how that would mesh with summer jobs or graduate courses that teachers are involved in.

The union has proposed a "clean sweep" approach to the 20 schools with poor results. That means that the academic initiatives that have accreted at these sites would be reviewed and ineffective ones junked. The district said it is willing to discuss that.

This round of bargaining for a 2011-2013 contrct is the first under a school board revamped in 2010 by a slate of candidates perceived as more friendly toward the union..