Developing confident graph users

These mistakes often reflect students’ uncertainty about how to communicate data effectively rather than a lack of scientific understanding. Fortunately, graph drawing is a skill that can be directly taught, practised and reinforced across the curriculum. Chemistry teachers can help students develop confidence by making graphing decisions explicit and discussing the reasoning behind them.

Specific ideas and examples

1. Choose the right graph

One of the first decisions is whether the data are continuous or discrete. In chemistry, measurements such as temperature, concentration, pH and reaction time are continuous variables and are usually displayed as scatter graphs with a line of best fit. In contrast, comparing the mean yield from different catalysts or different metals involves discrete categories and is better represented with a bar chart.

A useful classroom strategy is to give students data from several investigations and ask them to choose the most appropriate graph before plotting any data. I have used examples including cooling curves, rates of reaction and Hooke’s law from physics to give a straight line graph. The discussion is often more valuable than the drawing itself – for example, when students consider why that set of points requires a curve and not a straight line. This encourages learners to think about the purpose of the graph.

2. Scale selection

Choosing an appropriate scale is where many learners struggle. Encourage them to begin with the range of values and ask, ‘How can I make this graph easy to read?’.

Rather than telling students the correct scale for some data, present possible scales and ask which makes the best use of the graph paper and why. This develops judgement rather than rule-following. Students should also understand that scales do not always start at zero. Explicitly demonstrating this, such as modelling the same graph starting at 0 and at a more appropriate point can show clearly why this makes trends easier to interpret. Discuss potential pitfalls, such as difficulties finding a gradient or intercept – particularly at post-16 level.

The key is to reinforce that the graph tells the story of the investigation

3. The purpose of axes

Many learners remember to label axes but forget that the labels communicate the investigation. Encourage learners to ask ‘What is the relationship I’m trying to investigate?’.

Strategies include having a worksheet that allows learners to correct graphs by circling the errors or by re-drawing the line on pre-printed data. Or enable them to engage in meaningful peer review, marking to a set of criteria such as ‘correct plotting’, ‘correct scale’ and ‘correct labels’. The key is to reinforce that the graph tells the story of the investigation.

4. Lines of best fit

A common misconception is that every plotted point should be connected. Students need to recognise that experimental data contains uncertainty, so a line of best fit shows the overall trend rather than every measurement. Using the example of repeated measurements helps illustrate this. Encourage learners to consider the chemistry: the scientific relationship determines whether a straight line or curve is appropriate, strengthening both graphing skills and scientific reasoning.

Graph drawing is about making scientific thinking visible

5. Non-linear scales

Students often encounter logarithmic scales in mathematics before they appreciate why scientists use them. Chemistry provides authentic examples: pH is a logarithmic scale, while data spanning several orders of magnitude may be more clearly displayed using logarithmic axes. Explain and model explicitly pH with examples such as concentration versus time, or using the physics example of the decay constant, to show that scientists adapt scales to communicate data clearly when a simple linear scale is no longer appropriate.

Ultimately, graph drawing is about making scientific thinking visible. Understanding the reasoning behind graph choices helps learners develop conceptual understanding. By modelling the decisions behind good graphs, giving learners repeated opportunities to practise them, and reinforcing consistent expectations across subjects, teachers can help students develop a skill that supports practical work, data analysis and success in examinations.