S3 Geography — Population Structure and Dependency Ratios: Lesson Prep Guide for Tutors (four-step pyramid, ratio sums, four errors)

2026-11-12

Tutor lesson-prep guides · Junior Secondary Geography

Students look at a pyramid and say only that it is narrow at the top, and they divide by total population when asked for a dependency ratio. This lesson fixes three things: read the pyramid in four steps, divide by the working population for all three ratios, and turn the ratio into one sentence about ageing or a young population.

Objectives — By the end students can: (1) use four steps (read the horizontal axis, read the vertical age bands, compare left and right, compare base and apex width) to classify a pyramid as expanding, stable or contracting; (2) state that the denominator of a dependency ratio is the population aged 15 to 64, not the total, and compute child, elderly and total dependency ratios; (3) with a population of 5 million, 700000 aged 0 to 14, 3.5 million aged 15 to 64 and 800000 aged 65 and over, compute a total ratio of 42.9 per cent (child 20.0, elderly 22.9) and check that the two parts add to the total; (4) state one benefit and one cost of ageing with the ratio quoted, the benefit tied to labour or experience and the cost tied to health or welfare spending.

01 Prerequisites (3-minute check)

If any of these fails, fix it before the lesson starts.

Skill	Quick check	Pass mark
Percentages	What percentage is 700000 out of 3.5 million?	20 per cent
Addition	What is 700000 plus 800000?	1.5 million
Age bands	Which age band counts as the working population?	15 to 64

02 Lesson flow (45 minutes)

Time	Stage	Tutor does	Student does
0-6 min	Read one chart	Show a pyramid and ask only three questions: which side is male, what age the base is, and whether the place is young or old	Answer the three questions with reasons
6-15 min	Four steps	Model axis, age bands, left against right, base against apex, and name the three shapes with their tests	Repeat the four steps and name the shape
15-27 min	Three ratios	Write the formula, stress the working-population denominator, model child, elderly and total ratios	Compute three ratios and check that they add
27-36 min	Benefit and cost	Use the computed ratio to state one benefit and one cost, each in a sentence containing the number	Write one sentence with a ratio
36-41 min	Four errors	Show four wrong answers; groups say which step went wrong; the tutor adds only one line each	Explain one wrong answer
41-45 min	Exit check	Collect three questions, mark on the spot, name the act to reteach	Hand in three questions

03 Teaching script (read it out)

Scene 1: Act 1: Axis first, shape last

Reading a pyramid has four steps and the first is the horizontal axis: it shows population counts or a share of the total, with males and females on the two sides, so confirm which is which because getting it wrong reverses every later answer. Second is the vertical axis: age bands, usually five years each, youngest at the base. Third is left against right: a band where the two sides differ sharply shows a sex imbalance at that age. Only fourth comes the overall shape: a base clearly wider than the apex is expanding, widest in the middle with narrowing above and below is stable, and a base narrower than the middle is contracting. Students jump to step four, read “narrow at the top” and mislabel the shape, and often reverse the sexes. Markers want the four steps written out.

Axes first, sides second, shape last.

Scene 2: Act 2: The denominator is the working population

The only trap in dependency ratios is the denominator, which is the population aged 15 to 64, not the total. The reason is simple: the ratio asks how many dependants every hundred workers carry, so the bottom line must be workers. Child dependency is population aged 0 to 14 divided by the working population times 100; elderly dependency is 65 and over divided the same way; the two add up to the total ratio. With 5 million people, 700000 aged 0 to 14, 800000 aged 65 and over and 3.5 million workers: 700000 over 3.5 million is 20 per cent, 800000 over 3.5 million is 22.9 per cent, and 1.5 million over 3.5 million is 42.9 per cent, exactly the sum of the two parts. Make students run that addition every time; it is the best self-check available.

Workers on the bottom; the two parts add to the total.

Scene 3: Act 3: Turn the ratio into one benefit and one cost

Once the number exists it must become a conclusion, not “ageing is serious”. Model the sentence: an elderly dependency ratio of 22.9 per cent means every hundred workers support about 23 older people; the benefit is that many of them hold experience and savings and can keep working part time or volunteering, which adds to the labour supply; the cost is rising health and long-term care spending, which falls on a smaller working population. The common weak answer is “old people can help look after the family”, which is true but scores nothing because it is not tied to labour or the economy. Require one economic word in every benefit: labour, experience, consumption or savings.

Quote the ratio; tie the benefit to an economic word.

04 Question types and worked steps

Type	Example	Steps	Answer
Classifying a pyramid	A pyramid has a base clearly wider than its apex. Which type is it and what does that imply?	Read both axes; compare left and right; compare base and apex; classify as expanding with a high birth rate	Expanding, with a high birth rate and a large young population
Child dependency ratio	700000 aged 0 to 14 and 3.5 million workers. What is the child dependency ratio?	Write the formula; put 0 to 14 on top; put workers on the bottom; multiply by 100	20.0 per cent
Total dependency ratio	700000 aged 0 to 14, 800000 aged 65 and over, 3.5 million workers. What is the total ratio?	Add the two dependent groups; divide by workers; multiply by 100; check by adding the two parts	42.9 per cent
Effects of ageing	Elderly dependency rises from 20 to 22.9 per cent. Give one benefit and one cost.	Quote the change; tie the benefit to labour or experience; tie the cost to health or welfare; keep both sentences specific	Benefit: experience adds to the labour supply. Cost: higher health and care spending

Sanity check (teach this): Sanity checks: (1) the denominator is the population aged 15 to 64; using the total gives 30 per cent, which is plainly too low. (2) child plus elderly dependency must equal the total; if they do not, a figure was copied wrongly. (3) a ratio can exceed 100 per cent, meaning more dependants than workers, so do not call that an error. (4) a wide base is expanding while widest in the middle is stable; never merge the two. (5) benefits and costs must name a specific object; “it affects society” is not an answer.

05 Independent practice (3 questions)

Question	Answer	What to watch
Which step comes first when reading a pyramid, and why?	The horizontal axis, to confirm which side is male and which female	Whether the reason for the order is given
600000 aged 0 to 14 and 3 million workers. What is the child dependency ratio?	20.0 per cent	Whether workers are used as the denominator
Elderly dependency is rising. State one cost.	Higher health and long-term care spending, with a heavier load on workers	Whether the cost is specific

06 Common mistakes and what to say

Mistake	Student writes	Say this
Total population as denominator	1.5 million over 5 million is 30 per cent	The denominator is the 3.5 million aged 15 to 64.
Parts not checked against the total	Child 20 and elderly 22.9, total written as 40	The two parts add to the total: 42.9 per cent.
Shape read without the axes	Narrow at the top, so it is contracting	A wide base is expanding; read the axes before naming the shape.
Vague benefit	Older people can help at home	Tie the benefit to labour, experience, consumption or savings.

07 Homework (paper, section and question numbers)

Secondary Geography chapter index — Other chapters in this subject follow the same order; structure comes before distribution and urbanisation
Rework this lesson — Take one country pyramid, run the four steps and compute all three ratios
Lesson prep master index — Other subjects use the same numbers-first frame

08 Exit check (last 5 minutes)

Question	Answer	Decision
What is the denominator of a dependency ratio?	The population aged 15 to 64	Answering total population means reteach Act 2
What does a wide base indicate?	An expanding population with a high birth rate	Answering contracting means reteach Act 1
700000 aged 0 to 14, 800000 aged 65 and over, 3.5 million workers. Total ratio?	42.9 per cent	If not computed, reteach Act 2

09 Tutor FAQ

Can I teach the formula without the pyramid?

Do not split them. The formula handles numbers and the pyramid handles images, and both question types appear in the same paper, so teach them in one lesson.

Is a ratio above 100 per cent a mistake?

No. When dependants outnumber workers the ratio passes 100, for example 1.5 million dependants against 1 million workers is 150 per cent.

Does S3 need the five stages of the demographic transition model?

No. S3 needs only expanding, stable and contracting; the five-stage model belongs to the senior secondary population unit.

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A TutorZone lesson-prep guide. Written by the TutorZone team; questions and lesson flow are original and are not taken from any school or publisher material.