Do sixth forms make for better secondary schools?

27th November 2017 by Timo Hannay [link]

Does it help a secondary school to have an in-house sixth form? This is a question we're asked with surprising regularity, and though we've looked into it before we've never published the results; this post corrects that omission. For the time-deprived or attentionally challenged, here's a summary of the main findings:

• On average, secondary schools with sixth forms obtain better GCSE results than those without sixth forms.
• However, they also tend to have more able, affluent pupils and are more likely to be selective. Once these and other potentially confounding factors are taken into account, there is very little difference in GCSE performance between schools that have a sixth form and those that don't.
• There is, however, a big difference in post-GCSE destinations. Pupils at schools with a sixth form are much more likely to go to a sixth form (whether at the same school or elsewhere) and are correspondingly less likely to enter a further education (FE) college. This effect persists even after controlling for other factors. Based on these results, providing a sixth form in every secondary school might be expected to result in up to 20,000 more pupils each year choosing that route over an FE college. Conversely, separating all sixth forms from secondary schools might be expected to result in up to 50,000 more pupils every year going to an FE college.
• Thus secondary schools with integrated sixth forms do not enable greater academic success at GCSE, but they do encourage more academic educational routes thereafter.

A simple view

It's a common assumption that secondary schools with a sixth form (which account for about two-thirds of all secondary schools in England¹) are more academic and therefore produce stronger GCSE results than those that don't. Figure 1 shows that, based on a simple comparison, this is true. It uses recently released provisional results from 2017 GCSEs. Among all mainstream secondary schools in England (grey column), the average Attainment 8 score (the DfE's newish, broad-based measure of GCSE performance) was 46.5. But at schools with a sixth form (blue column) it was 47.5 while at those without (red column) it was 44.4. Since each point corresponds to roughly one GCSE grade, these differences aren't to be sniffed at: the gap between schools with and without sixth forms is roughly three grades per pupil. (Hover over the columns in this or any of the following figures to see the corresponding values.)

Looking at the more traditional 'five good GCSEs' measure, we see a very similar pattern, with a gap of more than 5 percentage points in the proportions of pupils achieving this threshold, as shown in Figure 2.

Even when we use pupil progress rather than attainment (in other words, when we allow for the fact that individual pupils start secondary school with different levels of ability), the same trend holds. This is shown in Figure 3, which uses the DfE's Progress 8 measure.

Yet even if schools with sixth forms do better, is this an indication that the presence of a sixth form itself causes better GCSE performance? Not necessarily, though there are reasons to believe it could. Maybe proximity to A-level students provides GCSE candidates with greater motivation or opportunities for peer-to-peer learning. Or perhaps schools with sixth forms can attract more highly qualified teachers.

So far so plausible, but the results shown above don't provide adequate evidence for this because schools with sixth forms are different in a variety of other ways too. For a start, all 163 grammar schools in England have sixth forms and it's hardly fair to compare pupil attainment at these academically selective schools with their comprehensive counterparts (though it may be fairer to compare pupil progress).

Like with like

Figure 4 compares the characteristics of final-year GCSE pupils at secondary schools with and without sixth forms (dark blue and red columns, respectively). Note that these data are from 2016 because 2017 numbers are not yet available. While the differences in sex balance are very small, schools with a sixth form have, on average, fewer pupils with special educational needs (with or without a statement), low prior attainment or from disadvantaged backgrounds, and more with high prior attainment or English as an additional language (usually a positive educational indicator). So even if the presence of a sixth form had no influence on the effectiveness of a school, we would still expect those with sixth forms to do better because, on average, they start off with more promising pupils.

To control for this, we created a third category composed of schools that have a sixth form but are in other ways as similar as possible to those that don't². These are shown in light blue in Figure 4. As you can see, they are much more similar to non-sixth-form schools in their proportions of pupils with special educational needs (without a statement), low or high prior attainment, social disadvantage and English as an additional language (EAL). Some discrepancies remain, most notably in the proportions of pupils with special educational needs statements, but these differences correspond to very small proportions of all pupils, and in general they are much smaller than the differences between non-sixth-form schools and all sixth form schools. We can therefore use this new group to revisit the differences in GCSE performance described above while largely controlling for these other potentially confounding factors.

Figure 5 shows the results of this comparison for Attainment 8 scores. Using provisional 2017 data, this all but eliminates the gap (ie, the red and light blue columns are almost identical).

The older 2016 data allows further slicing and dicing that isn't yet available for 2017. This shows similar patterns whether we look at attainment of boys, girls, disadvantaged pupils or EAL pupils. You can explore other metrics using the drop-down menu above Figure 5.

Figure 6, below, shows that this isn't just a result of using the relatively new-fangled Attainment 8 score. If we look at the old-fangled 'five good GCSEs' measure instead then we see much the same results in both 2017 and 2016.

Focusing more narrowly at whether pupils simply achieved A*-C grades in both English and Maths, the 2016 data also provide specific breakdowns for boys, girls, pupils with high prior attainment, pupils with low prior attainment, disadvantaged pupils and EAL pupils. We can also see a three-year average for this measure during 2014-16. In almost all cases any difference between schools with and without sixth forms is more or less eliminated when we control for other factors. Indeed, for pupils with low prior attainment it is schools with sixth forms that seem to do a bit worse. But this may be no more than a statistical artefact and is somewhat counteracted by an opposite result among EAL pupils. Overall, then, there is little to choose between schools with and without sixth forms once other factors have been taken into account.

The same is broadly true of the Progress 8 measure, as shown in Figure 7, though if anything, schools with sixth forms actually seem to do a bit worse whether we use the provisional 2017 data or the final 2016 data. This is also the case when we look in more detail at 2016 Progress 8 scores for boys, girls pupils with high or low prior attainment, disadvantaged pupils or EAL pupils. You can explore other measures using the drop-down menu at the top of Figure 7.

It's hard to know exactly what to make of this. Because the trend is consistent across different years, as well as various pupil and subject groups, it's unlikely to be a complete statistical artefact. Perhaps schools without a sixth form show slightly higher mean progress because they can give undivided attention to GCSEs. In any case, the differences are generally small so probably not worth taking too seriously.

Different destinations

The one big difference we found between schools with and without sixth forms is in the destinations data³, which is shown in Figure 8. (Note that the information here is two years older than the GCSEs data above because of the delay in capturing destinations after pupils leave school. So although the data presented were released in 2016 and 2017, they actually cover pupils who left school in 2014 and 2015.)

In 2015, the differences in the overall proportions of pupils going on to sixth form or a further education (FE) college are very similar across all groups of schools (roughly 87-88%). The distinction is the kind of further education they go into. In schools with sixth forms, the proportions going on to sixth form (whether at the same school or elsewhere) is almost 19 percentage points higher than at schools without a sixth form, and most of this difference – over 13 percentage points – persists even after controlling for other factors. In contrast, the proportions going to colleges of further education, which tend to be more vocational, are correspondingly lower. The figures from 2014 are almost indistinguishable from those in 2015. Furthermore, although disadvantaged pupils show lower overall rates of progression to further eduction, the relative levels of popularity of sixth forms and FE colleges is very similar.

This is no small effect. It is, of course, possible that pupils who already know at age 10 or 11 that they are destined for an academic route (regardless of their attainment levels or socioeconomic status) are preferentially selecting secondary schools with sixth forms. But it seems more likely that the structures of the secondary schools themselves are influencing subsequent pupil choice. This would imply that if all secondary schools had a sixth form then up to 20,000 more pupils each year might choose that route over an FE college. Conversely, separating all sixth forms from secondary schools could result in up to 50,000 more pupils going to FE colleges. This appears to be a good example of nudge theory, though here the consequences are perhaps closer to a shove.

Final assessment

So whether a pupil goes to a secondary school with or without a sixth form is, in itself, unlikely to affect their GCSE grades. But it may well influence whether their subsequent education is a primarily an academic or a vocational one. In short, institutional structures matter, though not always for the reasons that people assume.

Footnotes:

1. We analysed 3,118 mainstream state secondary schools in England. Of these, 2,136 (68.5%) have a sixth form and 982 (31.5%) don't.
2. Each school without a sixth form was matched to another schools with a sixth form. The latter was selected to be as similar as possible based on its proportions of boys and girls, pupils with high and low prior attainment, pupils who are eligible for free school meals, pupils with special educational needs (both with and without statements), and pupils for whom English is an additional language. In addition, London schools were only matched with other London schools (and similarly for non-London schools). Finally, grammar schools (all of which have sixth forms) were never matched as there are no similarly selective schools that don't have sixth forms. These matches were all made using 2016 DfE data. In the results presented here, the same sixth-form school could be matched against more than one non-sixth-form school; rerunning the analysis with the additional constraint that each sixth-form school could only be matched once did not change the results significantly.
3. In order to protect pupil confidentiality, the DfE suppresses some of the counts in its destinations data, especially where low numbers are involved. In these cases we use a variety of heuristics to estimate exact numbers. Though this inevitably generates small inaccuracies, we don't believe that these materially affect any of our results or conclusions.