The highest I've ever jumped was 3ft, It WAS by accident. No one told me that the horse I was using for my lesson tries to jump everything and anything if he can, someone left it set up and I was attempting to go around it but he overpowerd me and jumped it... needless to say I was on his neck. I learned my lesson the hard way to always take down the jumps.
Highest I've gone is like 2'3 or 2'6 not sure, the standards aren't marked at the barn I take lessons at. My position isn't very good yet though. But I think it's ok considering I've only been riding for 8 months :)