I think the better lesson is not, 'how many hours of homework is fair' but, 'teachers, please assign the minimum effective dose of homework'. This is one of the reasons I think labs are effective in high school science classes, provided they don't spell everything out for you and require you to understand what is going on, why you are doing it, and what's the important points are of what is going on. Applying knowledge is far more effective at making knowledge stick than balancing chemical equations.