Cover lesson · PSE / Well-being · Year 9 · Intermediate

Screen time and sleep: one pupil's two-week experiment

DCF: Citizenship → Health and well-being

Name: Class: Date:

Cover teacher — you need no subject knowledge

Print: this sheet, one per pupil. Lowri's sleep diary is printed below, so no computers or phones are needed; the same data is in sleep-diary-two-weeks.csv if you are in a computer room.

Run: 5 min read “What you are doing” and “What the experts say” aloud · 12 min Step 1 · 8 min Step 2 · 10 min Step 3 · 12 min Step 4 · 8 min Step 5. Total 55 minutes.

Collect: this sheet. Step 5 is private: tell pupils they will not be asked to share it, and do not ask anyone about their own sleep in front of the class. Lowri is invented; nobody has to talk about themselves.

If a pupil tells you they cannot sleep because of worry, something happening at home, or messages at night: do not discuss it in front of the class. Say “come and see me at the end”, take their name, and pass it to the class teacher or the school's safeguarding lead the same day.

What you are doing

Lowri is in Year 9 in Wrexham. She kept a sleep diary for two weeks. In Week 1 she did what she normally does: her phone stayed in her bedroom all night. In Week 2 she charged her phone in the kitchen from 21:30 and used an old alarm clock instead. You are going to work out how much she slept, compare the two weeks, draw the results, and decide how much her experiment really proves.

“Lights out” is when she turned her bedroom light off. In Week 1 she often kept using her phone in the dark after that.

What the experts say

The sleep medicine team at Evelina London Children's Hospital (NHS) says most teenagers need 9 to 9.5 hours a night, but the normal range is 7 to 11 hours. Getting less than 7 hours most nights probably means you are not getting enough.
They also say most people fall asleep within about 30 minutes, and that in puberty the body clock shifts later, so feeling awake at 10pm is normal, not laziness.
Their advice: stop using your phone at least an hour before bed, charge it anywhere but your bedroom, and avoid long lie-ins because they make it harder to fall asleep the next night.
The UK's four Chief Medical Officers (2019) advise: “Leave phones outside the bedroom when it is bedtime.” They also point out that research has found a link between heavy screen use and problems, but has not proved that screens cause them.

Step 1 — Lowri's diary

For each night, work out hours asleep (from “fell asleep” to “woke up”) and minutes from lights out to asleep. Careful when a time goes past midnight: from 23:45 to 07:00 is 15 minutes to midnight plus 7 hours. Write hours as a decimal: 7 h 15 min = 7.25. “Energy next day” is her own score out of 5.

Week 1 — phone in the bedroom

Night	Lights out	Last looked at phone	Fell asleep	Woke up	Woken by phone	Energy next day	Notes
Sunday	22:30	23:45	00:00	07:00	1	2	Scrolling videos in bed
Monday	22:30	23:30	23:45	07:00	1	2
Tuesday	22:30	23:15	23:30	07:00	0	3
Wednesday	22:30	00:15	00:30	07:00	2	1	Group chat about Saturday went on late
Thursday	22:30	23:30	23:45	07:00	1	2
Friday	23:00	01:00	01:15	09:45	1	3	Watched a film on her phone in bed
Saturday	23:00	00:45	01:00	10:30	0	4	Gaming online with cousins

Week 2 — phone charged in the kitchen from 21:30

Night	Lights out	Last looked at phone	Fell asleep	Woke up	Energy next day	Notes
Sunday	22:30	21:30	22:45	07:00	4	Phone charging in the kitchen from 21:30
Monday	22:30	21:30	22:45	07:00	4
Tuesday	22:30	21:30	23:00	07:00	3
Wednesday	22:30	21:30	22:45	07:00	4
Thursday	22:30	21:30	23:15	07:00	3	Worried about Friday’s maths test
Friday	23:00	22:30	23:30	08:30	4	Film downstairs with the family
Saturday	23:00	22:30	23:15	08:45	4

Step 2 — compare the two weeks

“School nights” are Sunday to Thursday: the nights before a school day.

Measure	Week 1	Week 2	Difference
Average hours asleep on school nights
Average hours asleep on Friday and Saturday
Average minutes from lights out to asleep on school nights
Total times woken by her phone (all 7 nights)
Average energy score after school nights

Step 3 — draw it

Draw two bars for each night: Week 1 shaded, Week 2 left white. Then draw a dashed line across at 7 hours and label it. Give the chart a title.

Step 4 — what does it show, and what does it not?

(a) Which difference between the two weeks is the biggest? Quote both figures.

(b) Compare Lowri's school-night sleep in each week with the expert advice. On which night was she below 7 hours, and what does its note tell you?

(c) After Friday and Saturday nights, how much later than 07:00 did she wake up in each week? The experts say long lie-ins make it harder to fall asleep the next night. Why might that be?

(d) Lowri says: “This proves phones ruin sleep.” Give three reasons why her diary cannot prove that on its own. Look at the notes column and at how the data was collected.

Step 5 — design your own test (private)

Nobody will ask to see this part. Plan a one-week experiment you could try yourself.

The one thing I would change
What I would record every night, and how
What I would keep the same so the test is fair
What result would tell me it had worked

Step by step

5 min — Read “What you are doing” and “What the experts say”.
12 min — Step 1: hours asleep and minutes to fall asleep for all fourteen nights.
8 min — Step 2: the comparison table. On a computer: =AVERAGE() over the five school nights.
10 min — Step 3: the paired bar chart with a 7-hour line.
12 min — Step 4: what the data shows and what it cannot prove.
8 min — Step 5: plan your own fair test, privately.

Success criteria

I can calculate time asleep across midnight and find averages that compare like with like (school nights with school nights).
I can draw a paired bar chart starting from zero, with a key, a title and a reference line.
I can compare real data with expert guidance and quote figures with their units.
I can explain why one person's two-week diary shows a link but does not prove a cause, using details from the data.
I can plan a fair test of my own habits, saying what I will change, record and keep the same.

If you finish early

Across the five school nights, how many extra hours did Lowri sleep in Week 2? Turn that into extra hours over a school year of 190 days, which is 38 weeks.
Thursday in Week 2 is her worst night of that week, even without her phone. Write two sentences explaining what that tells you about what else affects sleep.
Write a short, friendly text Lowri could send to her group chat explaining why she will not reply after 21:30. Keep it under 30 words.

If you want to talk to someone

Your form tutor, head of year or school nurse. Outside school: Meic, the helpline for young people in Wales, free and confidential in Welsh or English, 8am to midnight every day: phone or WhatsApp 080880 23456, text 07943 114 449, or chat at meic.cymru. Childline: 0800 1111, free and confidential.