Education officials across the country have replaced the principals and at least half of the staff in about 150 struggling schools to obtain federal aid, the Obama administration disclosed Thursday. In several hundred other cases, principals have been replaced and other major steps taken as part of the administration's unprecedented $3.5 billion campaign to rejuvenate thousands of the nation's lowest-performing schools. The initiative, which reflects President Obama's get-tough policy on school reform, is likely to be central to the coming debate in Congress over revision of the No Child Left...