slow progress in reading Yr 2

[Portamortar]

My daughter has just gone into Year 2 and the books she's been sent home with are the ones she was reading almost a year ago (set 6 on Read Write Inc).
They say that there is a regression over the Summer which I don't doubt. However, she was also put back 2 sets of books in the last term of Year 1 (from set 7 to set 5).
They say it's to work on fluency but she's reading the books she's been given really easily so I'm not sure if this is the right strategy.

I've brought it up with school and they've just blamed the summer holidays but for me, to be reading Set 7 books in February this year, then put back to Set 5 to work on fluency and now we're still on Set 6 - so behind where we were in February - suggests something isn't working.

Do you think I need to push the school more on this or is it really true that to improve fluency you just keep reading the easy books and don't move on to something that challenges you more?

I'm interested to hear views on this too, we're experiencing something similar. My DD has been much slower than her older siblings although the head teacher had said that the current Year 2 (and current year 8) were the two most affected by the Covid years, so I put it down to that and soldiered on. They also started using Little Wandle last year which she seemed to stagnate but they explained at the time it was not about moving up book bands.

She finished Year 1 on orange books which she could read (? Phase 6). Her class has been assessed for starting Year 2 and she came home excited saying she was now on blue books - which is two bands lower, I remember having some of the same books in reception/Yr1 (? Phase 4). I had that sinking feeling that despite keeping up reading through Summer we must be failing.

I am wondering if they are building confidence up/going back to basics or if on the day she was assessed she had a bad day. I am going to ask her teacher when I next see him. I will say though because the blue books are easy for she has started putting a lot of expression and voices in, so perhaps it is a good thing?