Is a weighted 4.2875 GPA above average for high school sophomore?

Yes, a weighted GPA of 4.2875 is significantly above average for a high school sophomore. Most high schools use a 4.0 scale as the unweighted maximum, so a weighted GPA above 4.0 indicates the student is taking and excelling in advanced courses (AP, IB, Honors, etc.). A 4.2875 GPA puts the student in the top percentile of their class.