I had Mr Lahti for three years. All upper level math classes, he was an amazing teacher
probably the easiest to understand math teacher i've had, his calculus class is definitely hard but he uses the curve so that it doesn't bring your grade down too much.
Lahti always found a way to answer any question in several ways, so that everyone would understand. VERY helpful.
Both of my years with Lahti were great. I didn't ever have him for anything other than calc, but in calc he is effective, challenging, and fun.
THE best math teacher. I asked him tons of questions and he was always nice about it, plus I got a 5 on the AP test.
Lahti's calc class was tougher than any other, he's a good & helpful teacher though...