There will be a huge variation, based mostly on age.
Once in Juniors, children won't be heard read regularly unless they struggle with reading.
For infants it is important,especially when they are younger, as regular practice enables progress.
It is hugely time consuming to hear all children read at school. As parents, you can listen daily and so ensure the level of practice necessary. Most schools simply can't manage that level of 1to1 and as long as you are doing it daily (and in my book, that means 7 days a weeks during term time and holidays for little ones...because the regularity is what makes the difference) then their reading will improve.
If you are concerned that the school don't know your child's level accurately as they don't hear them enough, write in and request that they are assessed as you think they maybe more able than the schools have levelled them....but be aware, it isn't just the physical act of reading, but expression, understanding etc too.
Junior age children should be reading aloud to an adult at home several times a week and also reading to themselves daily. Unless they struggle, they probably don't need to read to an adult in school more than once or twice a half term and only then, until perhaps Year 4.
One of the things that Private Prep schools often do,mis have the children read daily in class until about Year 1 or 2. They can do this because of the smaller classes and no of TAs or parent helpers. If the children are reading daily like this, plus daily at home too, they will progress faster. However, even if you are in a state school where they only hear reception read weekly, if YOU listen daily without fail, huge progress will still be made.
Parents are the biggest influence on reading. It is parents who can establish a love of stories by reading to their little ones and establishing a pattern of daily reading without fail,mso it is totally the norm and becomes a genuine love of the children. Only parents have 7 day a week access, every week of the year to their children to do this.
And for the older Junior aged child,don't give up reading aloud to them as an adult. People often stop around 7 when the children can competently read to themselves. Keep reading to them, and choose books just a bit differnt to those they would choose themselves,to broaden their horizons and introduce them to different genres. They will often then choose to continue reading such a book to themselves, which they would not have chosen themselves. It makes a huge difference in terms of movi g their reading and comprehension and vocab on.