we've had to complete it for my dd's school.
you didn't have to...
No. When it comes down to it, you don't "have" to do much. You don't "have" to put any clothes on but you might choose to, to avoid embarrassment or arrest. You don't "have" to send your kids to school. You can choose to home educate. When it comes to it, the only thing you "have" to do is eat, drink, sleep, breathe and excrete, surely?
That poster said she had to fill in in, presumably, because she was asked to and did.
The census day was Friday. OP presumably as the school had not had a return from you, refusing to answer the questions, they asked your daughter.
prh47bridge is spot on. The government is looking to close the gaps in attainment and I suspect if they find those students do not perform as well then funding streams will increase to allow schools to provide better interventions.
And if they are not underperforming then there will be no need. They can't use that information willy nilly. Data protection would prevent that.