Tables :: Attendance Tracking System - Adding Hours For Each Student Enrolled In Class Session

I'm creating an attendance tracking system, the attendance system needs to : Allow an instructor to enroll students into one or more classes, and then add attendance by date to each class(es). The problem that I'm having is, attendance is tracked by the number of hours that a student attends class. For instance, if class1 is in session from 8a.m. - 12p.m. student1 may only stay 2.50 hours of that class and student2 may stay 3 hours. The teacher needs to be able to add attendance to class1 for July 12, 2013 and add hours for each student enrolled in this class session who attended on that day. I have the following so far, minus the attendance:

Students -This is just the basic demographic information that instructors will need to enter on students.
StudentID (PK)
StudentLastName
StudentFirstName
DateOfEnrollment
LevelOfStudy
DateOfBirth

Location - These are the locations in which our students can attend classes
LocationID (PK)
LocationName
County
City
LocationPhoneNumber
LocationFaxNumber

Classes - These are the classes that our students can attend.
CRNNo (PK)
ClassName
LocationID
InstructorID

Instructor - These are the instructors that teach our classes.
InstructorID (PK)
InstructorLastName
InstructorFirstName
InstructorEmailAddress

Enrollment - This table enrolls the student into a class
StudentID(PK)
CRNNo (PK)
LocationID (PK)