RICHMOND -- Gov. Bob McDonnell's proposal to grade schools on the same A-to-F scale used for students has barely won General Assembly approval.Republican Lt. Gov. Bill Bolling cast a tie-breaking vote Tuesday to pass the bill in the 40-member Senate. The Republican-controlled House of Delegates approved the proposal Monday.McDonnell says an easy-to-understand grading system will encourage more parental involvement in schools. Democratic senators called the measure a gimmick.