In Harper Lee's "To Kill a Mockingbird", what was Scout's crime on her first day of school?

Actually, she "committed" two:

She showed the teacher that she already knew how to read (therefore undermining the teacher's role in Scout's education).

She explained to Miss Caroline why Walter Cunningham couldn't borrow a quarter (he wouldn't be able to pay it back), thus showing the teacher's ignorance to the "ways" of Maycomb folk. (Not to mention that she beat Walter up after school for having got her into trouble!)