With just 160 pupils, he believes he is 40 short of the magic 200 which has been mooted in government circles as the minimum size if a sixth-form is to be viable and provide the appropriate breadth of subjects.
But as a rural school with a catchment area of 100 miles, he believes his pupils would be forced to travel even further to one of the county's four further education colleges.
"One of the biggest concerns we have got is to ensure that funding is there to support the courses we operate for our students," said Mr Trobe, adding that he would be happy if funding for ndividual pupils were swapped for funding of courses.
"Our fear is, though, that this is a back-door route to squeezing sixth-forms out of schools, unless they are very, very big sixth-forms."
Mr Trobe's school receives around pound;2,700 per sixth-former, but he said he was aware of great disparities in levels of funding between different local authorities.
"We can say that we are slightly better off than some authorities and considerably worse off than others," he said.
"Some levelling up with the better-funded authorities would be very helpful."
He has already spoken to another Wiltshire school about linking up to offer sixth-form courses, he said.