Thursday 31 December 2015

2015 HSC results show how little effect the school has on student outcomes

Well, the 2015 HSC results are now out, and the usual 'school ranking' list made the front page of many Sydney newspapers, followed shortly thereafter by the usual disclaimers that the school rankings don't really mean anything. But that doesn't stop many parents thinking that getting their child into the 'right' high school from Year 7 will have a major impact on their eventual HSC results.

The actual results however, show that individual schools have very little influence on the results their students achieve -- the predominant factor influencing HSC results (in terms of % of 'Distinguished Achievement' (Band 6 or E4) subject results, and % 'All Rounder' (students with 10 units of Band 6 or E4 results in total)) is simply the ability level (as measured by the 'cut-off' selective entry test result to gain entry into the school) of the cohort of students that entered Year 7 six years earlier...

The figures below show that a school with a high 'cut-off' mark (selective schools entry test) to get into Year 7 will end up with a high percentage of Distinguished Achievement and All Rounder results when that group of students sits the HSC exam. For example, a school with a cut-off mark for entry of around 200-210 will end up with around 25%-45% "DA" and 5%-20% "AR" six years later. And a school with a higher cut-off mark (eg. 230-240) will end up with around 60%-75% "DA" and 30%-60% "AR".

The slight impact that a school can have is only apparent when a school consistently gets HSC results significantly above (or below) what you would expect based on the 'cut-off' score (ability level) that the students had when they entered Year 7. For example, NBSC Manly seems to consistently achieve slightly higher HSC results than would be expected from the 'cut-off' mark required to gain entry into Year 7 (However, even that may not be a 'real' effect - there are geographic reasons why some high ability students that might otherwise have gone to a selective high school with a higher cut-off mark decide to attend Manly. It's a long commute to get to James Ruse or Sydney Boys High from the Northern Beaches suburbs! So the correlation between 'cut-off' mark and average student ability level may sometimes be weakened by .local factors). And Sydney Technical HS seems to get a lower %DA in the HSC than one might expect from the entry cut-off scores for that cohort going into Year 7. But again, the %AR results for Sydney Technical are much closer to the expected range, so it might simply be that students choosing to attend Sydney Technical HS are not particularly strong in the compulsory English subject for the HSC, which might explain why the %DA results are depressed while their overall %AR results are more in line with the level of student ability.

[note: each school has four data points on the above charts, as the release of the 2015 results means I now how four years where I have the cut-off entry score and corresponding HSC results for that cohort]

These results also help to explain why private schools offer full and partial scholarships to attract students with high selective high school entry scores (and scholarship test score results, which are comparable) -- they are simply underwriting their future HSC results and school rankings.

It also becomes obvious why James Ruse will continue to come top of the school rankings (but might get pipped by Baulkham hills in a few years time), and which schools will continue to be at the top of such 'ranking' tables in future. You simply have to look at the current Year 7 entry cut-off scores to get a good estimate of the school's HSC results for 2021:

School (2015 cut-off mark for Year 7 entry):
Baulkham Hills (235)
James Ruse (230)
Sydney Girls (223)
Nth Sydney Boys (221)
Sydney Boys (220)
Nth Sydney Girls (219)
Hornsby Girls (216)
Fort Street (216)
Normanhurst (214)
Girraween (210)
NBSC Manly (206)
Sydney Technical HS (197)

One interesting side-effect is that selective high schools that do well in the HSC 'rankings' tend to become a more popular choice for parents choosing a school, so their 'cut-off' marks tend to increase, which in turn means a higher average ability level for the next cohort of students entering Year 7, and better HSC results five years down the track. This seems to be the trend at Baulkham Hills, and to a lesser extent at Fort Street.

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