Wednesday, March 30, 2011

Developing deeper understanding

Progress maps and outcomes have damaged mathematics in WA. By making distinct learning points without a web of links to outcomes, mathematics in WA has become disjointed and subsequently students lack fluidity between topics.

I doubt this is a new complaint and has been a fault of many attempted curriculum reforms, but it has been exacerbated by a renewed focus on assessment and the lack of credible assessment performed in early years.  In many cases a year 10 student can perform a percentage calculation if (and only if) it is preceded by 10 examples of exactly the same type.  A student can get 80% in their test by teaching study skills for a percentages test and by creating decent notes... but do they have an understanding of proportion and how it applies to percentages?  In many cases they do not.

As a teaching group we have been talking about percentages (as OBE pushed many decimal concepts into high school and they are now being pushed back by national curriculum). It is important to learn how to teach it more proficiently in lower school and to our lower ability upper school students.  One of the more successful ways we have encountered is to use relationships with ratios.

Problem: Find 50% of 50.

Using a ratios approach
100% of an object is 50
50% of an object is x

To get from 100% to 50% we have to divide by two (100% ÷ 50% = 2)

100% ÷ 2 = 50%
thus to stay in proportion
50 ÷ 2 = 25

Using a paper strip it is easy for students to see the proportions in action.

They can readily see that 50% is between 0 and 50.  It's easy to experiment with a wide variety to proportions and it readily extends to percentages greater than 100%, percentage increase, percentage decrease, finding percentages given two amounts and negative percentages.

Using a formulaic approach
Take the percentage, divide by 100 and multiply by the amount.
Take the amount, divide by 100 and multiply by the percentage.

I know which of the two approaches is quicker and easier to teach.. but to extend the formulaic approach to other types of problems requires new sets of rules to remember and apply.  Without a basis of understanding it becomes difficult to know which formula to apply and when to apply it (unless it was proceeded by a worked example - which leads us back to the original concern).

Using ratios and an algebraic approach
x ÷ 50 = 50 ÷ 100  (rewrite ratios as an equation)
x = 50 x 0.5  (multiply both sides by 50)
   = 25

Once students understand some basic algebra and proportion, the solution becomes trivial (as it is for many of us).  Sadly many students today do not reach this level of proficiency.  I'm sure there are other more effective and efficient ways to teach proportion and percentages (and even some that don't use pizzas) but I think my point is fairly obvious.

I think sometimes we can get carried away by the need to meet an outcome and teach the how (as is driven by a packed curriculum) rather than using an exploratory approach that provides students with understanding which can have lasting consequences (often unseen by those that don't teach senior school topics).  I originally saw the paper strip approach (or something similar) done by Keith McNaught at Notre Dame university.  It has stuck with me throughout my teaching.  When I am tempted to get curriculum dot points completed and tested (disregarding deeper understanding), it is always a good reminder of what should be done.

As a final note.. I do believe that nothing replaces practice and students need skills based work that requires rote learning (such as what is done with the formulaic approach).  Which means as teachers we have to get better at providing pathways through the why (such as via the ratio method and with formal proofs) into the how (such as with formulaic approaches) and then making connections to other techniques (as seen with the algebraic approach) - always remembering that students shouldn't have to re-invent wheels which in many cases took millenia to form.

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