Just to add, after discovering Clanchy as what was clearly an incredible poetry teacher, I then read the book about her teaching experience (after it had won the Orwell prize but before anyone had 'noticed'
the racism).
I didn't find the book racist, or ableist, or fattist. I'm Jewish and usually very sensitive to any hint of antisemitism in literature, but managed to not notice any here.
I think I was surprised it had won the award - but that's more down to what another poster described as its quite 1950s approach, it was definitely a book written by a white middle-class person for other white middle-class people, and presumed that the reader would not themselves have experience of being working class, or an immigrant, so she would need to explain it. Which as the child of refugees, felt kind of odd to me.
That said, what she was really writing about was the lessons she as a teacher and human being had learned about the class system and about structural racism in the UK. She couldn't have tackled those themes by not taking about the people impacted by them.
I think it is reasonable to argue whether a white middle-class person is the best person to make that point; maybe it would be better to get a member of an ethnic minority or a working class person to make those points themselves? But of course those books also exist, and it's had to criticise Kate Clanchy for that personally, given shehas dedicated her teaching career to amplifying the unheard voices of precisely those groups.
And one more point, albeit a minor one - I'm pretty sure she said the children she portrays are not only under different names but also in some cases composites. So I don't think it's as simple as one of the kids in it reading it and automatically thinking 'my teacher thinks I'm fat'. She will have taught thousands of kids at decades over multiple schools.