Schools seem to be moving towards longer lessons now. I think it depends on the DC. When DS2 went to secondary school I deliberately chose one with 35 min lessons. It was a boys school and as one maths teacher so rightly pointed out it mean't half an hour of hard work followed by 5 min pushing and shoving and general letting off of steam before another half hour of focused learning. Suited him to a tee.
I think I know this school
and yes it is brilliant for my sons too - they seem to take on more in 35 mins than many children I taught did in an hour. The last school I worked in moved to one hour lessons and it was desperate, truly awful and by lunchtime (which wasn't till 1.10 - just a ten minute break between 9 and then) many of the younger ones were hypoglycaemic and exhausted.
I have to attend some classes in higher ed and the best lecturer we had gave us breaks every half hour. What a huge difference that made to our ability to concentrate and take on board new concepts. For me, half an hour is optimum and any longer starts to operate on the law of diminishing returns.