The state's largest teachers union says it will sue state education officials in federal court today, claiming Ohio's charter school law violates constitutional guarantees of equal education for all students. Ohio Education Association spokeswoman Michele Prater says the lawsuit was spurred in part by a study on education inequities the union will release later today. She says the findings include that state spending on each student in a charter school is nearly double that for traditional schools. Education Department spokesman J C Benton says officials are confident the system is constitutional. Last year a Franklin County judge dismissed a lawsuit in which unions and school districts argued that charters were illegally created without consent of local school boards.