The best teacher that I've had is one of the teachers at my university lab.
He teaches Data Structures. We had some programming assignments and I was good at it, but whatever I'd do, he'd always find bugs, ask me to resolve it and he'd always give me challenges in the lab which is fun in the lab environment. University labs usually sticks to the sylabbus. I actually learned alot from that experience..

'Trail and Error is the best method to learn programming.'