Teachers at a St. Paul German immersion school voted Tuesday night by a large margin to affiliate with Education Minnesota, making them the state's only unionized charter school.

The 25 teachers at Twin Cities German Immersion School, a K-8 school, gave unionization 80 percent support.

The charter sector has been a difficult area for Education Minnesota to crack, despite near-universal unionization of traditional school districts. 

According to Chris Williams, an EM spokesman, three charters schools have unionized in the more than 20-year history of charters in Minnesota.  Two of those schools, near Hibbing and Forest Lake, later closed.  St. Paul City Academy, the state's first charter, also unionized, using the St. Paul Federation of Teachers contract, but no longer is union, Williams said. Another recent union drive at Ubah Academy in Hopkins stalled after teachers voted to organize but by the time a legal fight over the appropriate unit was resolved in court, participants had left the school.

EM President Denise Specht said that the group often hears privately from teachers about problem in their charter schools, and said the union can be a vehicle for them to speak out.

A study released this month at the University of Minnesota found that except for a one-year dip in student achievement during the unionizing process, unionization doesn't affect student achievement at charter schools.  That's based on California data from a 10-year period. .