My three children read exactly the same books in school even though they went to the school over a span of 10 years. Is that usual? Are there only a limited number of good novels about topics such as the second world war, or are schools not able to afford new ones?
Despite how it may look, there are advantages to school book stocks remaining constant, and several reasons why they do so. Many books don't age or diminish. Whether classics or "modern" classics, these titles are enjoyable and affecting from one generation to another. It would certainly be a pity if they were routinely let ago after a certain length of time.
However, set against that, for children not to have access to some of the best new writing of today is even more of a shame. While books last well from one generation to another, new books frequently pick up on contemporary issues and discuss them with a vigour and pace that is more likely to keep readers engaged.
In fairness to schools, and as you suggest, the most obvious reason for not changing stock is that it is expensive to do so. This impacts on books for whole-class reading more than it affects titles for personal choice. Typically, schools replace and so more frequently update paperback picture-book stock for younger readers, but tend to stick with the same books for Key Stage 2. This means that, in Key Stage 1, while favourite titles such as Quentin Blake's Mister Magnolia or Judith Kerr's The Tiger Who Came to Tea are still on classroom shelves, there is more chance that children will also get to know recently published picture books such as Jon Klassen's dark but brilliant I Want My Hat Back or Emily Gravett's hugely entertaining Again!, both published in the last two years and both already highly successful.
In Key Stage 2, the old favourites seem to stick around longer. Battered and sellotaped copies of Michelle Magorian's Goodnight Mister Tom, David Almond's Skellig or Louis Sacher's Holes abound in Year 5 and Year 6 classrooms. All are wonderful books for the age and stage and, in the case of Goodnight Mister Tom, it is hard to think of a better way to learn about a central part of the history curriculum. But I think teachers and pupils – and parents, from the sound of your enquiry – would also benefit from refreshing stock more frequently.
That leads to the second reason why the choice of titles may remain rather passive. Given everything else they do, teachers have very little time to keep up to date with new writing. Rather than buy something untested that might disappoint, it is easier and safer to stick with what has worked before. Of course, there are ways around this, and many teachers take them. If they are lucky enough to be near any of the exceptional independent children's bookshops that bring the best new titles immediately to the attention of their readers, they may have good access and sound advice.
Otherwise, they can follow prizewinners. Sally Gardner's Maggot Moon scooped the Carnegie Medal last month following winning the Costa children's book award earlier in the year. The Guardian Children's fiction prize has eight brilliant titles on it, some of which are for Key Stage 2, with more for Key Stage 3. Last year's winner, The Unforgotten Coat by Frank Cottrell Boyce, is set in a Year 6 classroom, which makes it a perfect class story for that year group. The new books are there; they just need to be found and matched to the school, class or individual reader.