Since I got straight A's (in the days before A existed) without doing a lot of HW, I'm very sceptical about it. Especially in Y7-Y9*
I think the bright kids who pick things up easily may get less benefit from HW. Mine on the other hand, (who needs time to poke around, go over and approach from other angles before things click into place) is now a "not so far from" straight A student BECUASE of the homework.
It's been evident that where quality homework is set and gets done well (not rished, half arsed) he masters and retains the topic. Not so much if it isn't or he makes a lazy pig's ear of it.
By the latter half of last ac. year he settled into the different educational culture and was pretty much consistent with doing his homework well.
He went back to school yesterday, one piece of homework (freer extensive writing) handed in and marked already. The difference between what he was prepared to do and could produce last year and this is dramatic. The school is great, the lessons are well planned and engaging, the teachers approachable and good at their jobs. But what has made one of the most dramtic contributions to his all round improvement is the expectation he will put his back into homework, take charge of his own learning and hone his skills via practice.
I'm not skeptical that some children find it a useless time consuming bother that doesn't add much to their education. However I don't believe they are the majority. There are more Bog Standard Somewhere Around the Average kids than there are children at either extreme. For those boringly averageish kids engaging, quality homework and the expectation that it will be done, and done well, can make an enormous difference.
I've done a complete 180, I hated homework and wished it at the bottom of the ocean when he was at Italian state cos there was far too much of way too little real value. Now he's at a British school I regard it as one of the fundemental supoort pillars of his his education. Cos when a school hits the right standards in terms of well thought out, quality tasks and spreads the load accross the week so it doesn't become a daft sized burden, bloody hell what a difference it can make.