I’m going to take a guess and say that you’re from Texas.
Here is the law regarding the 90 percent of attendance:
Texas Education Code 25.092(a): A student may not be given credit for a class unless the student is in attendance for at least 90 percent of the days the class is offered. The board of trustees of each school district shall appoint one or more attendance committees to hear petitions for class credit by students who are in attendance fewer than the number of days required under Subsection (a). Classroom teachers shall comprise a majority of the membership of the committee. A committee may give class credit to a student because of extenuating circumstances. Each board of trustees shall establish guidelines to determine what constitutes extenuating circumstances and shall adopt policies establishing alternative ways for students to make up work or regain credit lost because of absences.
To sum it up, the law says that you must attend 90% of school days but there are ways to get around that. If an attendance committee views your situation as having ‘‘extenuating circumstances’’ then they could give you credit. If you haven’t been approached by your school regarding your attendance, I would not worry about it. They will contact you and explain things to you if it gets to the point that you are referred to the attendance committee.
Source for the law: http://law.onecle.com/texas/education/25.092.00.html