IQ isn't used for anything anymore. We know now that it's really hard to measure, and also that it's not the predictor of future success we once thought it was. MOTIVATION is a more important factor.
I don't know how you get into advanced level classes. But the criterion is not so much performance on standardized tests as much as it is -achievement-, which would be reflected in your past grades. Advanced level classes are a lot more work, and what they really show is that you're able to do a lot more work!
If you don't count specialized or technical careers (doctor, engineer, architect, etc.) most jobs are available to anyone with any degree. Employers want to see a college degree primarily because it shows you're able to complete something difficult, you're able to keep up with the workload and jump through all the requisite hoops.