Here are our school's enrolment numbers for the last five years:

210, 216, 220, 226, 230

What do you think next year's number will be? Have a good guess before we work anything out.

The interactive shows five past years of enrolment as bars. We will calculate the mean together, then watch where a dashed mean line sits compared with the last bar. We will find three different ways to predict next year, and a second chart adds the prediction bars on the end.

Here are our five years on the chart again: 210, 216, 220, 226, 230. Now we place a sixth bar for next year.

Now use the three methods on real schools' numbers, working in your copy, one method per line.

Then this comparison:

• Douglas N.S. (Cork): 300, 298, 302, 296, 300. These numbers wobble up and down. Find the mean, then say whether the year-to-year step suits this school or misleads you.

Stretch (if you finish early): for either school, write which one prediction you would put on the school newsletter, and why.

Before you write, study this worked example for Ballybane N.S. so you know exactly what a full journal entry looks like.

Ballybane N.S.: 180, 188, 196, 204, 212

• Mean prediction: 196
• Step prediction: 220
• What-if prediction (20 pupils leave): 200

Trusted prediction: the step method, 220. Why: the numbers climb by the same amount each year, so the year-to-year step fits this school best.

Now pick ONE of the two schools. If you pick Douglas N.S., use this what-if: what if 15 extra pupils join next year? Start from the prediction you trust (mean or step) and adjust it by 15.

In your maths journal write:

• your three predictions (mean, step, what-if);
• the single prediction you trust most;
• one sentence saying why that method was the most confident for this school.