Like all introductory quantitative courses at Columbia, Stat W1211 kind of sucks. The way the curriculum is structured, there simply isn't the time to explain concepts, so a bunch of unintelligible formula and theory is shoved down your throat. That's my impression, at least. Do you best early on to understand what's going on - not just the formulas, but the big picture. The textbook didn't do that for me; I recommend YouTube videos. Given that the course is rough, Heng is probably your best bet. Compared to the other teachers I sat in on, he has the best English and the most motivation to help you understand. His lectures are pretty focused and clear, and follow powerpoints that you have access to on courseworks. He's pretty reasonable, and just do you best and pray for the curve to help you out.