It is probable that these factors are linked. In the public sector an institution that is more efficient does not use its surplus to declare a dividend. It uses it to invest in improved quality and choice for its users. So, colleges that are more efficient offer a greater range of options to learners and are able to invest more in both facilities and support services.
There is, however, an important qualification. The benefits of scale come from large numbers of students doing similar sorts of things. A sixth form college with 2,000 students doing A-levels therefore is in a very important sense "bigger" than a general FE college with twice as many students split between 14 programme areas. This gives an important twist to the specialisation debate -perhaps it is not focus that achieves results, but scale.
We need to think about the implications of these facts for policy.
Ministers came into office saying "standards not structures" were what mattered. Yet in recent years they have swung back towards structural reform with proposals for specialist schools, academies, foundation schools and competitions for new sixth-form provision. What light can research shed on this debate?
We know, from work for the Learning and Skills Council on the funding gap, that it costs more to educate 16 to 19-year-olds in school sixth forms than in colleges; the difference is substantial and is unlikely to be eroded for several years even though ministers are committed to a level playing field.
We also know that, when differences in prior attainment are taken into account, schools perform no better than FE or sixth form colleges.
These two facts alone ought to suggest caution before embarking on an expansion of school sixth forms.
More recently, in answer to a parliamentary question, Bill Rammell, the Minister of State confirmed that the performance of school sixth forms was directly related to their numbers on roll; the larger the A-level cohort the better the results.
The Learning and Skills Network will shortly publish two further decisive pieces of evidence that support the case for consolidation post-16 rather than further fragmentation.
A study of the potential for economies of scale (Size Matters, Owen, Fletcher and Lester) shows that larger institutions reap substantial benefits from their ability to optimise class size. They are able to use these efficiencies to invest in improved resources and more choice for learners.
Typically, a large sixth form college will offer more than 40 subjects at A-level compared with a minimum of fewer than 20 in smaller institutions.
Crucially, the authors suggest that diseconomies of scale begin to operate powerfully for sixth form groups of fewer than 200; yet Ofsted reports that the average size of school sixth forms is 173.
A second study by the National Foundation for Educational Research (Do Post 16 Structures Matter?) looks directly at the impact of local systems of education on participation and achievement.
Researchers examined whether the types of post-16 institutions in an area affected outcomes. Is staying on post-16 better in school sixth forms; or where everyone has to go to a tertiary college; or where one can choose between schools, general FE and specialist sixth form colleges?
Once background variables such as social class, prior attainment and sex were taken into account, researchers found little difference between systems; though the presence of grammar schools, and in some areas, of school sixth forms, was associated with lower staying on rates.
The message is that bringing in new providers is unlikely to raise participation significantly. There is one more factor to consider.
Differentiated institutions lead to social segregation. New analysis of the Youth Cohort Study, by Geoff Stanton, senior research fellow at the University of Greenwich, shows that different types of institution post-16 attract very different sorts of learners.
School sixth forms focus almost exclusively on A-levels. But schools and colleges are also differentiated in terms of their social class composition, levels of prior attainment and the ethnic mix of students.
For education institutions to reflect local populations is an important and desirable aim in itself. When a segregated system is also a less efficient one the argument against it is unanswerable.
Mick Fletcher was until recently research manager at the LSDA and is now an education consultant