If they have severe and on going needs and are working significantly outside their age an EHCNA would be appropriate.
An EP would be able to unpick what’s going on using a battery of tests. I use Ravens progressive matrices to compare non verbal reasoning and ability to define words. Very interesting. You’d likely need this evidence as part of assessment anyway.
Have you considered working memory, developmental language delay (DLD), dyslexia and strategies used with these? Working memory affects everything as does a language disorder and links to specific literacy (and often numeracy) difficulty. Specific assessment of language eg the CELF might highlight issues.
Working significantly outside year group expectation may unlock non-ehcp high needs funding in some local authorities
Tbh no intervention removes the barrier to learning – kids who are behind got that way because learning is harder for them. We can give them strategies, but we can’t take those reasons away. That’s why they end up on intervention year after year.