How do people have GPA's above 4.0? How do the same people bomb the SAT/ACT?

<p>I understand that Honors/AP classes enable someone to receive above a 4.0, but how do students have 4.8''s and 5.0's? My school doesn't do rankings or GPA (out of 4.0) so I'm honestly confused.
My follow up question is how a student can have above a 4.0, and then not even score in the 90th percentile for standardized testing? And yes, I understand some people aren't test takers but they must do fine on tests in their classes.
I feel like I've missed something important and or this site has induced a form of paranoia within me.</p>

<p>1) If you make the high end of the range high enough, you can get the mean up significantly. My D’s school weights AP classes as A=6, and pre-AP (same track, but not the right grade to be AP) as A=5. </p>

<p>2) US schools don’t limit As to the top 10% of the nation. Even if grades correlated exactly to test scores, an A average would not equate to 90th percentile test scores.</p>

<p>My school has a 6.0 weighted GPA scale, which means that a 100 or a 99 in an AP/Honors course would be a 6.0 or 5.9 respectively. Meanwhile, a 100 or a 99 in a level course would be a 5.0 or a 4.9 respectively. I’ve seen schools do the same thing, except on a 5.0 scale as well.</p>

<p>

 
2 words: grade inflation</p>