I have jumped up to 3' in a group lesson, but it was all advanced riders and horses. I agree with what everyone else has said... talk to your instructor about why you're not jumping higher. Maybe there are some things they think you need to perfect before moving up, or maybe you are in a group that's too low level for you. I know when I teach jumping at the lower levels it is a pain in the neck to have to re-set courses and heights on the jumps for each rider when you want to make sure everyone gets ride time and you're on a schedule.
Good luck!