I help out with reading in year 1.
The bottom end are children who are still (at this point in year 1) reading red and pink books - these are the sort with short repetitive sentences
Sam saw a parrot
Sam saw a hat
(where there is a picture of parrot and hat)
The middle of the class are on ORT about level 4-5 - 2-3 sentences on a page.
The top of the class are on chapter books, whole complex paragraphs etc.
dd2 is in this class, she isn't at the top, and I am not bothered. ds was slow to get reading, he took off in year 3, he is now year 6 and heading for level 6 sats and has passed 11+
dd1 was good early reader, but was quite in school, so was always on school level about 3 behind where she could actually read until she was about year 2/3.
Bearing in mind that some kids are 12 months older than others, and some kids are early readers and some kids have lots of parental support, there will be a huge variation.
Moat important thing is that you read regularly at home, that you still read out loud to your kids, books that are further on than they can read for themselves, (this helps with vocab building) and that you model reading to them too.