I'm glad the advice was helpful:).
FYI, I have seen this kind of attendance policy before. Here in Fairfax County -- at least in 1985-1989 when I was in school -- the policy was as follows:
A student is tardy to class if they are not in their seats when the bell rings.
If the student is more than 20 minutes late, and there is no parental or doctor's note or something similar, this is an unexcused absence.
If the student has 3 unexcused absences in a class, they receive a zero for the course for the year.
If the student is tardy four times, the student also receives a zero for the year.
A draconian policy , perhaps. Perhaps it wasn't enforced the way it was written, but I never tried to find out! :)