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The RSC was on the Today programme yesterday, lamenting the lack of mathematical rigour (and indeed science, they claim) in modern science exams. Reading a bit more about that story let me to this story, about a study the RSC ran last year setting modern pupils questions from a variety of eras. They did not do well - an average of 25%.

I had a look through the questions and was pleased that I'd be able to answer most of them (I seriously fall down on organic chemistry!) If I'm ever very bored, I may sit down to attempt the whole thing and see how I do. Just looking through it, though, I was struck by the fact that almost all of the questions are set in units of decimetres-cubed but want answers in cm-cubed.

This seems rather pointless to me: a student who can do the unit conversion will be able to do it throughout the paper while a student who can't will fail throughout. Thus quite a significant fraction of the marks are essentially binary - you get all or none. From a pedagogical point of view, it would seem more useful to have one set of marks allocated to a number of different unit conversions and then to allocate the rest of the marks to concepts in chemistry. (It may be that I was captured by the system - I worked for a few months at the National Foundation for Educational Research, who set the SATs being criticized by the RSC)

I discussed this with [livejournal.com profile] shreena, and her contention was that this is useful preparation for further science and life because it teaches you to read carefully for units. This is a fair point, but would surely be better managed if the paper used a variety of different units throughout - meters cubed, litres, even millimetres cubed.

What do other people think? I must confess that I may be partially biased because decimetres cubed is (from a physics perspective) a non-standard unit, so it appears as if the test is being deliberately obscure. I have a feeling that chemists use it more commonly, so maybe it's just a question of scientific culture.

Date: 2009-11-08 12:09 am (UTC)
From: [identity profile] kht.livejournal.com
Decimetres-cubed seems like a very odd unit to me. Why not just call it a litre?

I can see the point in training students to be careful with units - perhaps they're deliberately trying to catch out students who aren't reading carefully enough. But if that were the case, I'd expect them to use different units in different questions.

How does the marking scheme work - do you just lose one mark for failing to get the units right, or lose all of the marks for not giving the right numerical answer?

Date: 2009-11-08 09:47 am (UTC)
From: [identity profile] vectorious.livejournal.com
I would say that this tests exam technique and not science. I would say that you have a right to expect standard units in virtually every situation that you come across in science, and if you did come across decimetres cubed this would be highlighted and have a reason.

I remember in one section of my professional exam there was a a multiple choice question that was identical to one in the example book they gave you, except that rather than a single negative it was double negative. I felt at the time that this was purely an exam technique question as it was testing spotting the double negative rather than knowledge of the subject.

Date: 2009-11-08 06:14 pm (UTC)
From: [identity profile] midnightmelody.livejournal.com
Just got home, and got 4 hours sleep last night, so forgive me if this is garbled.

It's a standard chemistry conversion and convention, and pretty important for most analytical chemistry (so I'd argue that it's reasonably valid as a test construct to allot quite a high proportion of questions to include this). Also, most chemistry students wouldn't see the unit conversion as the same question, because it arises in a variety of contexts, at different stages - to some extent this rewards students who 'transfer' procedures appropriately, and this is generally a good thing to reward in exams.

In practice, my only concern is whether there were any students who fell down because of this conversion being needed - and this would have been lamented continuously in Examiner's Reports if this were the case - both A levels and GCSEs tend to self-correct from year to year in this fashion.


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