Children often find it difficult to judge how much new information they have covered and say they haven't covered anything new, when in fact they have.....and after covering something, can't always remember accurately if it was covered for the first time or not. That's worth remembering.
Most subjects have building blocks. In any year group, you never start with brand new material and don't re-visit some of the prior knowledge or building blocks. In Year 7 quite a lot if this is needed with children coming from many different schools, but they will be going further than previously too. In some subjects they will cover all new ground and in some subjects some old ground and some new ground. It's also worth remembering that because you are looking at something you might have looked at before, this isn't wasted and it's actually necessary to cover things several times to gain a secure grasp of them. This 'inter-leaving' of topics - regularly returning to topics covered previously, recalling them, seeing connections to new topics and re-visiting over and over again over time, rather than just in a big cram for an exam at the end of the year, is current educational thinking. It's about making knowledge and understanding secure.....and having covered something once in primary in Yr4 or in Y6 doesn't make it secure.
I had a DC go to a Prep where they did several years of quite serious French and couple of years of Latin, as well as some Maths and Science beyond KS2 stuff. Once in Yr 7 of their next school (also independent and with probably half and half state and independent intake) they started French and Latin from the beginning....they were advantaged and their prior knowledge gave them confidence, but they did learn new things in each topic and certainly re-I forced their knowledge and skills. It was the same in science and some topics had been covered before, but some were covered in greater depth and some covered in a different way. Learning was definitely going on. It's too simplistic to say 'done that before, therefore waste of time and no new learning happening'. As I said at the start, children often find it hard to pinpoint exactly what they've learned which is totally new and what they have learned which is deepening understanding of topics already covered....actually, it's often the more able who can see which work is harder and can see where learning has happened, and those who are weaker who think they've done everything before, in the same way, it's often weaker students who think every test is easy, because their understanding isn't there to recognise when something actually is difficult.
In every year, absolutely rightly, chunks of time are spent re-visiting and embedding knowledge and skills. It is vital. More of it will happen in Yr 7 if everyone is new. Don't think learning isn't happening.