To me a student's grade is only final on the day I have to turn in quarter grades. A grade is a constant evolving representation of the students understanding of the content for that quarter. For me a bad grade on an assignment only means the assignment needs correcting (more understanding is needed). It might reflect poorly on the overall grade at that moment but if the student isn't satisfied with that they can do something about it. That means if a student is not happy with how their understanding is represented by their grade they can always try to improve it. The best way and most significant way to improve their understanding and therefore improve their grade is by making corrections to the performance assessment that is worth 60% of their grades. All other work is final unless a discussion is had with me. The biggest weighted percentages are going to have a greater impact on the grade because they represent a student's understanding of the content.