My 11 year old pupil, who began last summer not knowing the two times table, and reading at a level around that of an eight year old, has just got L5c in a maths practice test, and L4a in English. For readers outside the UK, the nationally expected standard is L4, or 4b to be sure of it. We still have a lot of work to do to build fluency and confidence in writing and spelling, but the improvement began with building up his knowledge of patterns and procedures in basic maths, and of English grammar. We did not accept approximations, but explained everything clearly to him first and then made him practise, even when this was not his idea of fun.
The result is that, faced with, say, calculating the perimeter of a shape, or its area, he knows how to do the additions and multiplications required without expending his mental energy on them, and can instead think about what the question is saying and how to answer it. He knows what verbs are, why simple grammatical terms are as they are, and how they function in writing. In other words, he can do his work with confidence, approach secondary school knowing that he is not set up to fail, and enjoy his football without thinking he should be doing more homework.
Perhaps most important, he now agrees with me that he is an intelligent boy - not necessarily the quickest, but intelligent - and no longer thinks he is stupid.