Let pupils settle and find their own pulse first; the neck (carotid) is usually easiest. Some will not feel it straight away, so reassure them and let them try the wrist too.

Keep this light: it is just the curiosity beat. Take a few guesses out loud, then move on. Do not hand out stopwatches or set up the investigation yet.

This table is the pupils' on-screen content. Read the two short paragraphs first, pausing to point at your own chest for the heart's size and place. Then read the two table rows one at a time, asking a pupil to give their own example for each before you reveal the one on screen. Keep the reading in small chunks so it never feels like one long block.

You will introduce the fair test idea hands-on in the next two steps, so it is deliberately left out of this table to keep the load light here.

Head off the common misconception that the heart is on the left side; it sits in the middle, tilted slightly left.

A bit of the story: scientists once thought the heart warmed the blood. We now know it is a pump, which is why Irish public-health advice tells us to keep active to keep the heart strong.

Model the full cycle out loud at the IWB: I wonder… I predict… I will keep this the same… I counted… I think…. Demonstrate counting your own pulse for 15 seconds against the class clock, then a short burst of marching, then count again.

Make every beat visible so groups copy the prediction and the conclusion, not just the counting. Say the conclusion sentence aloud word for word. Stress the fair-test idea here: one thing changed, everything else kept the same.

Drive the interactive on the IWB. Five cards appear — the activity, how fast the heart beats, the counting time, who counts, the stopwatch. Sort them with the class: the activity goes to Change, how fast the heart beats to Measure, and the counting time, who counts and the stopwatch to Keep the same.

Be clear about which decision is genuinely the group's and which is modelled. Modelled together: we all change the activity and measure the pulse, because that is what the question is about. The group's real choice: which activities they line up to compare, and how many (two, three or four). Let groups make that choice on their own FairTestPlanner page; you only set the theme of comparing activities.

Push the desks back to make space. Pupils who should not exercise are the timekeepers and recorders, never left out.

Pick one delivery model and stick to it. If you have floor space for every group at once, call the 15-second counting windows from the front so the whole class counts together. If space is tight, do not front-call windows: instead let groups take turns in a marked-off area, each timing its own 15-second count with its own stopwatch while you move between them. Choose one before you start so the timing stays consistent.

Watch for miscounting: model finding the pulse for the slower counters before they start.

Explain the middle value simply: line your three counts up smallest to biggest and take the one in the middle. When two counts tie (e.g. 19, 19, 25), the tied value is the middle, so circle that. Mind anyone who feels light-headed and let them sit down.

Collect a resting figure and a busiest-activity figure from a few groups on the board. Draw out the pattern: the heart beats faster the harder the body works.

This is display-only science-talk; pupils do not type anything. Steer the talk toward heart health: regular activity keeps the heart muscle strong, which matches current Irish advice to stay active each day.

Look for:

• pupils linking a faster pulse to muscles needing more blood
• groups noticing that repeating made their results steadier
• any group whose results were odd, and asking why

Keep this brisk. Ask one pupil to say in their own words why the pulse sped up, and one to say why we took the middle value.

Homework idea: ask pupils to feel their pulse at home before and after running up the stairs, and tell the class which was faster.