Some families consider moving house specifically to access a grammar area. The economics and the timing matter enormously.
The short answer
For relocation to work: you must move into the catchment area before the application deadline (typically October of Year 6), and you must be able to evidence the address with utility bills and similar.
The longer answer
Schools and councils are alert to address fraud. Short-term rentals timed to the application window are routinely investigated and offers can be withdrawn even after acceptance.
Property prices in the most popular grammar catchments (Bucks villages, Trafford, parts of Sutton) carry a meaningful premium for catchment access. This is real value but it is also priced in.
What experienced parents do
For families relocating in good faith and with time: ideally move in Year 4 or earlier. This gives the child time to settle in the new primary, build local friendships and minimise disruption.
What to avoid
Avoid: short-term rentals or address-of-convenience strategies. Beyond the fraud risk, the child's emotional disruption is real and the gain from grammar entry is hollowed out by an unsettled secondary start.
Practical next step
Talk to a local solicitor about the address evidencing requirements before signing any lease. Different councils have different rules; what passes in one borough may not in the next. A small, deliberate action this week is worth more than a grand plan for the year ahead.