Sunday, 2 June 2013

Fractions – is that pizza for me (slice 1)?

Another fraction of a pizza
Have you ever wanted to improve the pupils learning and your teaching of fractions? I have and I have probably taught fractions the same way as everyone else, but I still had children who did not fully understand what a fraction is, just like everyone else. How many metaphorical pizzas have been used each day during Maths lessons up and down the land? Yet our pupils have the same misconceptions year after year, despite using their favourite food. What is the problem? What was I doing wrong? What is to be done?


The problem

If you give a diagram like the one below and ask the question what fraction is shaded? What fraction is unshaded? How many children would give the answers 2/8 and 6/8, probably most, but can they make the leap to ¼ and ¾? They find this really difficult and need lot of questioning and prompting to see the equivalence.




Another issue is when you ask a student to share 4 chocolate bars between say 5 friends and ask how much do they each get. It takes some time before a 12 year old for example realises it is 4/5. (Perhaps I am being a bit optimistic there.)


As the pupil get older they are introduced to ratio. Do they ever see the link between a ratio of 2:3 and the fractions 2/5 and 3/5?


Different categories of the whole

Reading an article from the nrich website ‘Teaching fractions with understanding: part-whole concept’ really made me reflect upon how I had taught fractions over the years. The suggestion, as I understand it, is to explore fractions in different situations. Think of the quantities, the types of ‘whole’ where we ask the children to find fraction of it. Like me you’ve probably used questions like find 3/5 of 400kg with varying success. It is easy to teach them the method but do they really understand it?


The article suggests that we should think of the quantities, the wholes as being categorised as four different types, ‘discrete wholes’, ‘continuous wholes’, ‘definite wholes’ and ‘indefinite wholes’.


Discrete wholes

This is such things as beads, counters, bricks etc. Objects which are not normally broken up

Continuous wholes

This category lends itself to food, examples that you could use include Pizzas, Pies and Cakes. What did we do before Pizzas?

Definite wholes

This is where the universe on which we are working is defined but made up of different objects. Like the diagram below which is made up of white, yellow and blue rectangles.


Indefinite wholes

‘Indefinite wholes’ are made up objects which have no apparent beginning or end, you could present them with a picture of a string of beads but with both ends continuing into the distance or as in the article quoted a diagram that looks like the one below.

 The whole thrust of this analysis is to give children different experiences of what constitutes a ‘whole’. From this stand point they can then progress to finding a fraction of a whole and appreciate the part-whole relationship.


My next blog will discuss what we can do in the classroom to promote deeper understanding of fractions and the part-whole concept.


An excellent book on children’s misconceptions is by Doreen Drews

'This practical guide to children’s common errors and misconceptions in mathematics is ideal for anyone training to teach 4-11 year old children and keen to gain a deeper understanding of the difficulties children encounter during their mathematical development. The book is structured around National Curriculum Attainment Targets, and deals with individual misconceptions, in each case providing a description of the error, and an explanation of why the error happens.'