In Wales spending per pupil fell by 5%, the report, published yesterday, said.
The IFS said the higher cuts in England were driven by bigger drops in local authorities and school sixth form spending alongside faster growth in pupil numbers.
The 8% cut, calculated by the IFS, includes additional effects of much larger cuts to school sixth form spending per pupil (25%) and local authority spending (55%).
In Wales, the cut in total school spending has also been driven by cuts to sixth form spending (22%) and local authority spending (38%).
Luke Sibieta, IFS research fellow, said: “School spending per pupil has fallen by more in England than in Wales over the last eight years, virtually eliminating the gap in spending per pupil between the two countries.
“Policymakers in both England and Wales have chosen to protect spending directly allocated to schools for pupils under 16, and to make much larger cuts to sixth form allocations and to local authority spending.”
Responding to the IFS analysis, Geoff Barton, general secretary of the Association of School and College Leaders, said: “The facts could not be more plain.
“The scale of these cuts is a devastating indictment of [the government’s] commitment to education and has put educational standards in jeopardy.
“Schools and colleges urgently require additional funding, but neither the chancellor nor the prime minister seem to be alert to the crisis which has developed under their watch.”
The Department for Education has been contacted for comment.