How the family tie actually works
The Statutory Residence Test decides residence through automatic tests first, then the sufficient ties test, which weighs your UK days against up to five ties. The family tie is one of them. You have it if your spouse or civil partner, or a partner you live with, is UK resident for the year, or if a UK-resident child under 18 is here, but for the child limb only if you spend time with that child in person in the UK on 61 days or more in the tax year. A parent who visits for exeats and a handful of weekends stays well below 61 days; a parent who effectively lives here in term-time does not.
The full-time education exception
There is a specific carve-out for boarding-school children. A child who is UK resident, under 18 and in full-time education in the UK is disregarded for the family tie if they would not be UK resident but for that education, and they spend fewer than 21 days in the UK outside term-time. HMRC's guidance treats half-term breaks and inset days as part of term-time, so the 21-day count runs on the genuine holidays, which for most families means the child flying out for summer and Christmas rather than staying in the UK. Kept within those limits, the school itself creates no family tie at all, and your own position falls to be tested on your other ties and days.
Why one tie can still decide the year
The reason the question matters is the ties table. A leaver, someone UK resident in any of the three prior tax years, becomes resident with three ties at 46 to 90 UK days, two ties at 91 to 120 days, and just one tie at 121 to 182 days. So a family tie on its own is harmless at low day counts but decisive at high ones, and it rarely travels alone: accommodation available to you for 91 days, 40 or more UK work days, more than 90 UK days in either of the two prior years, or the country tie each add to the count. Parents structuring a school arrangement around leaving the UK should fix the day budget and the ties together, not the school plan first.
Get the ties counted properly
The family tie rules are precise enough that a defensible answer usually exists, but they punish guesswork, and the work tie or an available property is often the real risk hiding behind the school question. Horizon UK Tax Solutions runs full SRT reviews, including school and family arrangements, on a fixed fee agreed upfront; book a free 30-minute clarity call before the school year starts.