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Teacher guide — Grade 8, Unit 4: Showing data

Time: 3 lessons + project (about 5 periods). Track: A (no-code); optional CODAP.

# Lesson Time
1 Bar charts and dot plots 40–45 min
2 Line graphs and pie charts 40–45 min
3 Misleading graphs 40–45 min
P Unit project: Graph gallery 2 periods

Before you start

  • Materials: Graph paper, rulers, coloured pencils; optional computers with CODAP.
  • Read docs/pedagogy/lesson-anatomy.md and docs/pedagogy/ai-use-policy.md.

If you have no computers / no internet

All eight units run on paper, calculators and the blackboard. Computers are optional (spreadsheet or CODAP, https://codap.concord.org); every activity below has a paper version.

Common misconceptions

  • Using a pie chart for numbers that are not parts of a whole.
  • Starting a bar chart's axis above zero makes small differences look big.

Differentiation

  • Support: give a partially filled table / sentence starters; pair with a data-steward role.
  • Stretch: ask "what would change your conclusion?" and "who is missing?"

Answer key (check questions)

Lesson 1: Bar charts and dot plots 1. Which graph suits 'favourite subject'?
Answer: A bar chart (categories). 2. What can a dot plot show that a table hides?
Answer: Where values cluster, gaps and unusual values. 3. What must every graph have?
Answer: A title, labelled axes with units, and a sensible scale.

Lesson 2: Line graphs and pie charts 1. Which graph shows change over days?
Answer: A line graph. 2. Walk 12, bus 5, cycle 3 of 20: percent who walk?
Answer: 60%. 3. Why would a pie chart of 'minutes by student' be wrong?
Answer: The values are not parts of a single whole.

Lesson 3: Misleading graphs 1. Axis starts at 48 instead of 0 — effect?
Answer: Small differences look huge. 2. Name one more way to mislead with a graph.
Answer: Uneven scale, cut-off data, 3D, cherry-picked time period, misleading title. 3. What is the first thing you check on a graph?
Answer: The axes: what is measured and where they start.

Assessment

Starter quiz each lesson (3 questions, one recalling the previous lesson); unit quiz in quiz.yml; project marked with the rubric in docs/pedagogy/assessment.md; 2-minute oral check per group.

Alignment

Extends the Grade 8 compulsory Maths statistics chapter (pie chart, mean, median, mode) with question-forming, data collection and interpretation.

Answers: practice exercises

  1. (a) bar chart (b) line graph (c) dot plot or histogram (d) pie chart or bar chart (parts of a whole).
  2. A histogram's x-axis is a continuous number line (classes follow each other with no gap); a bar chart's categories are separate.
  3. Bars in order Maths 12, Social 11, Nepali 6, Science 5, English 2; axis from 0.
  4. Total 36: Maths 120°, Social 110°, Nepali 60°, Science 50°, English 20° = 360°.
  5. Rounded: 6.5, 6.5, 6.5, 7.0, 7.0, 8.0, 8.0, 8.0, 8.5, 8.5, 9.0, 9.5. Two clusters (6.5–7 and 8–8.5), one high value (9.5); range 6.5 to 9.5 hours.
  6. 13.8 − 4.8 = 9.0 percentage points; it fell to about 4.8/13.8 ≈ 0.35 of its 1990 value, i.e. by about 65% (roughly two-thirds). Teach "percentage points" vs "percent" carefully.
  7. Looks like enrolment tripled or more; actual rise is 20/980 ≈ 2%. Honest version: bar chart from 0, or a line graph clearly labelled with a note.
  8. Doubling height also doubles width, so the picture's area is 4 times bigger; the eye reads area.
  9. Bar chart (or pie: three parts of one whole). Bars ordered Mountain, Hill, Terai (natural order) from 0; Terai tallest. Remind students the numbers are synthetic.
  10. Peer-share a few; reward reviews that mention axes and source.

Real-data exercises: notes

  • R1 Arrivals grew over the period with dips (e.g. around the conflict years in the early 2000s); students should look up the events rather than be told. Air arrivals are the large majority. If the downloaded file's years differ from the title (listing says 2001–2014, description 2003–2014), use that as a lesson in checking files.
  • R2 OWID values (downloaded 2026-10-11), child mortality %: 1990 — Bangladesh 14.6, India 12.7, Nepal 13.8, Sri Lanka 2.3; 2020 — Bangladesh 3.1, India 3.3, Nepal 3.0, Sri Lanka 0.7. Sri Lanka lowest throughout; the largest fall in points is Bangladesh (11.5) and Nepal (10.8). Values may change slightly with OWID updates.
  • R3 Right-skewed: tallest bar at 4.0–4.4, long tail to the right toward 7.8.