GPA: Schools weigh GPA differently. One thing I saw was that some schools with honors / AP you can get above a 4.0 to the point of a 5/4. Also GPA can be messed up when someone has a bad home life, or works a job.
honors/ap/ib: These are often related to which school you go to. Poor schools have few to no AP classes available. My school had 2 AP courses available, 0 IB. I was shocked when I went to college and talked to people that had 10 or 20 AP classes. Sure anyone can just take the AP exam, but I didn't know that at the time.
Extracurriculars: Bad and poor schools have fewer extracurriculars.
When you compare good schools (which are in wealthier more exclusive neighborhoods) with bad schools, not even accounting for private schools, its absolutely astounding the differences.