I hate to be the recalcitrant one on this post, but the teacher is full of it.
My son has been in a private, independent school since he was two. By the first grade, he had already had two years of foreign language and was doing an hour of assigned homework a night.
Now, he is entering ninth grade and will have 3-4 hours of homework per night. He also plays on the Varsity football team, is an active Eagle Scout, is in student government, was in a school play, and will wrestle and play hockey this fall/winter.
He is an A/B student in school and had the opportunity to take the SAT early through Northwestern University last year due to high standardized test scores.
He is not any different than the rest of his classmates. They all just learned how to budget their time and work hard starting at an early age. Based on the matriculation and scholarship dollars, I think the edge they get from a rigorous homework schedule is an outstanding way to progress through school.
At the same time, I think your son would have been successful regardless of how much time he spent doing his homework. And I don't think he's going to be able to keep all of that up through high school, either.
I'm an engineer by profession, and I work in a senior management role in an engineering firm. When I make hiring decisions, I am far more impressed by a prospective employee who worked an after-school job for 3-4 hours per day at the age of 16 than one who did 3-4 hours of homework every night.
You are correct. So much of what kids learn and achieve is just about raising their expectations. Treat them like losers or delicate flowers - and thats how they will turn out.