Does your high school link attendance to earning a certain grade on a semester exam to receive credit for a course?

We are investigating implementing a policy which links attendance to semester exam grades.  If your school has developed such a policy, please share your policy... the pros and cons, etc.  We are looking at implementing the following:  If a student has 11 or more excused and/or unexcused absences (including a combination) in one semester, the student must achieve a 70% or higher on the semester exam to receive credit for the course.  Excused and/or unexcused absences are accumulated on a per class basis.