The government does not expect a significant impact on the number of pupils attending private schools.
It estimates that around 37,000 students will move to the state sector over the long term, but believes class sizes will not increase.
It points to research by the IFS which says it would be possible for the state sector to “easily accommodate extra pupils” because overall student numbers are set to fall by 700,000 by 2030.
That drop is larger than the total number of children currently attending private schools.
However, pupil numbers are not falling by the same amount everywhere, so some individual state schools could face pressure on class sizes.
The Independent Schools Council (ISC), which represents more than 1,400 private schools, says some of its members reported a 4.6% fall in Year 7 pupils in September 2024.
The ISC believes the government has underestimated the level of pupil displacement that will be caused.
In October 2024, the organisation said it would press ahead with plans for a legal challenge against the policy. It argues the tax changes breach the European Convention on Human Rights on two counts: the prohibition of discrimination, and the right to education.
The Treasury said it would not comment on potential litigation.
