Graph drawing is an important skill which is tested in some form in many science GCSE qualifications. It is important to teach pupils good graph drawing skills as early as possible and to give students plenty of opportunity to hone these skills in lessons.
A good technique is to set out the graph drawing process as a series of questions to guide students towards being able to set up their own axes in the future.
What type of graph do I need?
Pupils should be able to draw line graphs, bar charts and pie charts. In choosing which type of graph to use, ask pupils to consider the two sets of data they hope to represent. If both sets of data consist of numerical values, a line graph is usually the appropriate choice. If one set of data is categoric and therefore consists of words (for example name of metal) then a bar chart is usually the best choice. Pie charts are used to represent proportions, for example the amount of each metal found in an alloy.
Which variable goes on the x axis?
It is important to remind pupils which axis is which, for example by stating “x is a cross (across)”. In an experiment, the independent variable (the thing you changed) always goes on the x axis and the dependent variable (the thing you measured) goes on the y axis. If pupils find it hard to remember which is the independent variable, one way to work it out which works for most practicals is to ask pupils which column of the results table they can fill in before the experiment (the independent variable) and which do they have to wait until during the experiment to complete (the dependent variable).
What scale should I use?
Many pupils find it hard to draw the scale along their graph axes. Consider the ability of pupils when deciding how much assistance to give at this stage. The important point to stress is that the scale should look like the markings on a ruler, with evenly ascending numbers. Pupils should identify the minimum and maximum measurements from their data, and should work out how best to represent the range on the graph paper.
Pupils should always be reminded to include labels on both the x axis and the y axis, and where appropriate they should also include the units used for measurements.
How do I plot the graph?
Before pupils become confident in their graph-drawing skills, it is a good idea to take five minutes to draw an example graph: an excellent opportunity to make good use of the interactive whiteboard. Demonstrate how to find the correct places on both axes and combine that information to locate the exact position of each point. Encourage pupils to use a pencil to plot points, and to use an x rather than a dot for maximum accuracy.
How do I draw a line of best fit?
Pupils really struggle with the concept of a line of best fit. Try to explain that the line of best fit represents what the graph would look like if all the results were entirely accurate. It follows the general pattern of the results, so it may be a straight line or a smooth curve, but not a wiggly line or dot-to-dot. It is best to demonstrate what you mean before pupils attempt their own lines of best fit. Straight lines must be drawn with a ruler, and should have about the same number of points above the line as below it.
Differentiating for low ability pupils
If your class is a low ability set, they may need more assistance at first. Consider printing out a template for the graph for pupils to draw on. Depending on pupils’ ability, you could start by drawing the scale on the template for them and just leaving them the labelling and the plotting to do. As pupils become more confident, reduce the amount of assistance given. Make use of any teaching assistants and ensure they are fully briefed before the lesson.