In 2015 it became a legal requirement for young people in England to stay in education, training or employment until 18.
In recent years, there have been between 15 to 32 Scilly children in each post-16 year group, with two year groups completing their sixth form education at any one time.
Children in the City of London - the only other local authority with no post-16 provision - can get a bus or tube to a nearby provider but island children have no choice but to travel to the mainland.
Where they live during this time is causing tensions between the council and parents - and it can also come as a culture shock to the young islanders.
"I have to get the boat or the plane, if I get the boat it gets in quite late so I have to stay the night in Penzance, then it's a six or seven hour train to Winchester," says Jacob, who has just finished his college studies.
Before starting college, the longest time he had spent off Scilly was about two weeks: "I'm used to walking down the road and knowing everyone but on the mainland, I don't know anyone and it's a bit weird."
Accommodation options include staying with host families, costing about £9,000 a year; boarding, with the nearest state boarding costing £16,500 per year - or imposing on mainland family and friends.
This does not include travel or other incidentals and families say the sums have been increasing "exponentially" as the cost of living goes up.
Parents can get a grant - increasing this year to £9,635 - to help with travel and accommodation costs.
Jacob's mother Samantha Mallon says: "Any raise in the money is welcome, but it's still so far short of what we need and it's not addressing the safeguarding issues."