PSLE Science Experiments & Experimental Questions: CER Guide for P5 & P6

📅 Last Reviewed: July 2026  ·  ✍️ By: PSLE Hero Editorial Team

Experimental questions appear within Booklet B, the 40-mark structured section of the 2026 PSLE Science paper. Students need to identify variables, interpret data, evaluate methods, and communicate a clear explanation. Use this guide alongside the main PSLE Science revision guide.

1. The Three Types of Variables

Every scientific experiment described in the exam has three distinct variables. Identifying them correctly is the first step to answering experimental questions:

• Changed Variable (Independent Variable): The single factor that is deliberately altered to test its effect. An experiment must have only one changed variable to be a fair test.
• Measured Variable (Dependent Variable): The factor that is observed or measured to collect results (e.g. height of seedling, time taken for ice to melt).
• Controlled Variables (Constant Variables): All other factors that must be kept exactly the same throughout the experiment. If any of these are changed, they could affect the measured variable, making the test unfair.

2. The Purpose of a Control Setup

Examiners frequently ask: "What was the purpose of Setup B (which does not contain the independent variable)?"

The answer must follow this strict phrasing template to secure full marks:

Example: Seed germination setup where Setup A has damp cotton wool and Setup B has dry cotton wool.

• Measured Variable: Germination of seeds.
• Changed Variable: Presence of water.
• Purpose of Setup B (Dry Cotton): "To act as a comparison to show that the germination of the seeds is solely due to the presence of water (and not other factors)."

3. How to Describe Trends

When asked to describe a relationship or trend based on a table or graph, use the "As... increases, ... increases/decreases" structure.

• Example trend: "As the distance of the light source from the plant increases, the number of bubbles produced per minute decreases."
• Common Trap: Do not just state the numbers (e.g., "At 10cm it was 50 bubbles, and at 20cm it was 30 bubbles"). Explain the overall pattern.

4. The CER Answering Method for Booklet B

For explanation questions in Booklet B, Claim-Evidence-Reasoning (CER) is a useful practice framework. It helps students connect their answer to the data and the relevant science concept; CER is not an official SEAB marking formula:

Element	What it means	Example Phrasing
Claim (C)	Directly answer the question (choose an option or make a statement).	"Material X is the most suitable material for making the helmet..."
Evidence (E)	State the specific data or direct observation from the graph or table.	"...because it can withstand a force of 500 N before cracking, which is the highest force among all materials."
Reasoning (R)	Connect the evidence to the scientific concept. Explain why.	"This shows that Material X has the highest strength. Therefore, it will not break easily when hit, protecting the user's head."

5. Reliability vs. Validity

Students often confuse these two terms when evaluating experimental designs:

• Reliability (Is it consistent?): An experiment is made more reliable by repeating it multiple times and calculating the average results. This minimizes the impact of random errors or outliers.
• Validity (Is it a fair test?): An experiment is valid if it actually measures what it intends to measure. This requires keeping all variables constant except for the changed variable.

6. Common Student Mistakes in Experiment Questions

Even students who understand the concepts lose marks because of these recurring errors in Booklet B:

• Vague Purpose Statement: Writing "to see which material is better" instead of the required phrasing: "to act as a comparison to show that [measured variable] is solely due to [changed variable]."
• Naming Too Many Changed Variables: Stating more than one changed variable in an experiment. Every experiment in the PSLE tests only ONE changed variable for it to be a fair test.
• Confusing Aim and Purpose: The aim of an experiment states what is being investigated. The purpose of a control setup states what it proves by comparison. These are different questions with different required answers.
• Ignoring Units: When citing evidence from a table or graph, always include units (e.g., "5 cm taller", "20 degrees Celsius", "3 bubbles per minute") instead of just writing numbers.
• Vague Relationship Descriptions: Writing "the plant grew more" when asked for a trend. Always use the structure "As [changed variable] increases, [measured variable] increases/decreases."

7. Marks Scoring Checklist for Experiment Questions

Before submitting your answer for any experimental question in Booklet B, check these four points:

1. Have you named the correct variable type? (Changed / Measured / Controlled — use the exact PSLE terminology).
2. Is your control setup purpose phrased correctly? ("To act as a comparison to show that [measured variable] is solely due to [changed variable].")
3. Have you cited a specific value or observation as evidence? (Never write general facts without linking to the question's data).
4. Have you used a linking word to connect evidence to your conclusion? ("Therefore", "This shows that", "As a result").

---

→ Privacy Policy  |  → Data Deletion Request  |  ← Back to Science Tips  |  ← Back to Home