The exam is sat partway through Year 8, so the realistic preparation window is Year 7 and the first half of Year 8. That is earlier than most families expect.
Why starting earlier matters
Starting earlier is not about covering more content. It is about having time to build reading speed, vocabulary, and mental arithmetic, which genuinely cannot be crammed.
If you are already close to the exam
That is not a disaster. It just changes the plan: technique and timed practice give the fastest return when time is short.