"It is very easy for a sixth form to become parasitic on a school. We spend a lot of time in senior management deciding whether to run some courses or not.
"Once you withdraw a key subject because it is uneconomic you risk losing other subjects. It's a slippery slope" Norman Corner is the head of Lady Lumley's School in Pickering North Yorkshire, one of four schools singled out for praise in the Office for Standards in Education report Effective Sixth Forms.
Lady Lumley's is a small school of 830 pupils with 150 in the sixth form. It offers 17 A-levels, (above OFSTED's minimum of 12 ) one advanced general national vocation qualification - in business studies - and a comprehensive and innovative range of additional studies including minority languages, first aid and survival cookery for those going on to university.
OFSTED describes how "appropriate measures" are taken to reduce the cost of subjects taken by few students, such as combining Year 12 and 13, reducing the number of taught periods and combining AS and A-level courses.
Norman Corner tells of how the school had kept its music A-level going one year, despite there being only one interested pupil. "She was determined to do it," he says, "so she began the A-level course immediately after finishing her GCSEs in Year 11 with a lot of one-to-one tuition, and in September she joined those studying for music in Year 13 and took the exam one year early. It was the only way."
Peter Howell, Lady Lumley's head of sixth form, is aware of the dangers of withdrawing subjects. He says: "If you withdraw a subject and a pupil goes elsewhere, then you reduce numbers in other subjects, it has a knock-on effect."
However, small groups have to be counterbalanced elsewhere. Mr Corner has laid down that the sixth-form staffing budget must not be exceeded by more than 2 per cent.
More than half - 55 per cent - of the school's pupils stay on into sixth form, many attracted by careful guidance, supervision and the responsibilities Lady Lumley's affords. Sixth-formers are encouraged to help with reading schemes lower down the school and with outdoor education with Year 8.
Tracey Young, aged 18, wants to study law at Nottingham University and for work experience spent time with the Crown Prosecution Service. She had considered the nearest college where she could have studied law A-level but decided to carry on through the school. She says: "We know the staff here and we get good results."
Northallerton College, some 40 miles away, is also praised by OFSTED for having a large, diverse and effective sixth form.
A 14-19 community college with 950 full-time pupils, 380 in the sixth form and 2,500 part-time students, John Bell, the headteacher decided some years ago that the school needed to tighten up its accounting procedures.
The school offers 17 A-levels, GNVQs through franchises with local colleges, many courses for adults including national vocational qualifications and a part-time postgraduate certificate in education. Sixth-formers are encouraged to take a mix of GNVQs and A-levels and A-levels such as law and psychology have to be studied in adult evening classes. .
Joanna Todd, aged 16, came to Northallerton to take an advanced GNVQ in health and social care and A-level English literature. She said: "I couldn't have done this combination elsewhere. I want to be a nurse but I wanted to study English lit as well for my own interest."
Income for each year group is closely monitored and the college uses a spreadsheet produced by a local consultant and similar to that produced by inspectors to analyse costs. Cash is allocated to each department on a formula basis.
By having a clear idea of the desired unit cost for each qualification, Mr Bell has been able to calculate, for example, that the local college was failing to give adequate financial support through its franchising arrangement. Northallerton now aims to make its own arrangements. Mr Bell says: "It became clear if we were to offer such a varied curriculum post-16, then we would have to take a very systematic approach to costing it out."