Wisconsin Department of Public Instruction:

In classrooms across Wisconsin, students learn mathematics, reading, social studies, art, science, and other subjects through integrated projects that show great promise for increased academic achievement. The catch: the collaboration between students and teachers often involves multiple academic subjects, which can present licensing issues for school districts.
“There is no question that parents and students want innovative programs,” said State Superintendent Tony Evers. “The reality of some of today’s educational approaches requires that we look at our licensing regulations to increase flexibility and expand routes to certification to ensure that these programs are taught by highly qualified teachers.”

Related, by Janet Mertz: “An Email to Madison Superintendent Dan Nerad on Math Teacher Hiring Criteria”