Had this battle from reception at DCs school.
Was told it's about establishing phonetics and chunking etc. We dutifully complied and read the books each week but also did our own bedtime reading.
Year 1 we disengaged completely but we went under the radar as focus for teacher is on those who can't read, not those who can!
Year 2 (current) DD was assessed and reading/comprehension were beyond the reading scheme they were using (beyond expected level at end of year 6).
but...DD STILL gets upper end of Yr2 level books sent home weekly.
I don't mind as they are usually non-fiction so she is learning about something new. We have an unspoken agreement with teacher that DD reads the school books on her reading day with teaching assistant. Assistant makes comment in her log book (always 'excellent' with no follow up) and we do our own thing at home.
Home reading is much easier now, as we don't actually do very much other than get DD to read out loud (she reads a chapter to us at bedtime) and we check comprehension by asking what she has just read. Or we help ad-hoc with a word she's not sure about (was 'Prometheus' yesterday as she was reading 'Horrible Histories - Greek' in the back of the car).
Her reading has come on leap-and-bounds this year (has finally stopping insisting on reading everything out loud) and it's a joy to have a child who will sit quietly in the back of the car and read!
Occasionally we write in school log book 'DD read Beast Quest 25-30 over half term and is currently reading Goth Girl. Just so they know she is constantly reading outside of school. She prefers to read books for 7+ age group, rather than the books for 11+, as she is only 7. She just reads them very quickly so you need to have lots of books at hand! Don't worry too much about pushing into older books - they won't necessarily be interested in the themes.
Don't waste time butting heads with the school and get a library card (I order all Beast Quest series from the library otherwise I would be bankrupt)!