Database design for attendance feature
I would suggest something different than you have here- a separate table to record the student_class relation:

| student_id | class | date       | 
-----------------------------------
| 2          | 7     | 2013-10-24 | 


This would have one record for a student where a class was attended. For each class and date for which there is no record, it can be seen that the student did not attend.

If you want to further normalize the design, I would suggest instead three new tables:

Student_Class: (to determine enrolled students)    

| class | student_id     | 
--------------------------
| 1     | 2              |


Class_Date: (class_date_id surrogate key for pk(class, date)) (to determine dates classes  were held)

| class_date_id | class | date       | 
-----------------------------------
| 1             | 7     | 2013-10-24 |


Student_Class_Date: (to determine which students attended which class period)

| class_date_id | student_id     | 
----------------------------------
| 1             | 2              |


This would allow you to easily define which classes were held on which date, easy updating etc. 

Edit: Added additional detail with student_class implied relation from question context