To explain a process, give each step and the reason it comes where it does. A list of steps shows memory. A reason for each step shows understanding.
This lesson is part of SPM subjects and learning resources. It combines well with interpreting information in a technical diagram.
What is the step-and-reason method?
For each step, write three short parts: what is done, why it is done, and what it makes possible next.
| Part | Sentence starter |
|---|---|
| What | “First, the formwork is built…” |
| Why | “…so the wet concrete keeps its shape” |
| Next | “…which allows the reinforcement to be placed” |
Not every step needs all three parts, but every step needs a reason.
Worked example: casting a small concrete slab
An original question: Explain the sequence for casting a small ground slab. (5 marks)
List answer. Formwork, reinforcement, pouring, compaction, curing.
This has the right order but earns few marks for an “explain” question.
Reasoned answer.
Formwork is built first so the wet concrete holds its shape and thickness. The reinforcement is then placed inside the formwork, because steel bars must sit at the correct position before concrete surrounds them. Concrete is poured next, and it is compacted so trapped air is removed and the slab is dense. The slab is finally kept moist during curing, so the concrete gains strength slowly and does not crack from drying too fast.
Each sentence gives an action and a reason. The words “then”, “next” and “finally” carry the order.
The mistake that costs marks
One slip is to give the steps in the wrong order, such as pouring before the reinforcement is placed. Another is to give steps with no reason.
| Error | Why it loses marks |
|---|---|
| Pouring before reinforcement | Steel cannot be placed inside concrete that is already poured |
| Steps with no reason | Shows recall, not understanding |
| Skipping curing | Strength gain and cracking are left unexplained |
To test each step, ask “What goes wrong if this comes first?” The answer to that question is usually your reason.
Using connecting words
Short connecting words make a sequence read as an explanation. Useful ones are: first, then, so that, because, which allows, finally.
Keep each sentence to one step and one reason. A long sentence that joins three steps is hard to mark and easy to get wrong.
Check yourself
Explain why a trench for a pipe is backfilled in layers that are compacted one at a time. (3 marks)
Answer
Soil is placed in thin layers so that each layer can be compacted properly, since a thick layer cannot be compacted all the way through. Compaction removes air spaces, so the soil settles less later. The ground over the pipe then stays level and the pipe is better supported.
Notice that each step has a reason: thin layers allow compaction, and compaction reduces settlement.
What to study next
Practise sequences with the original mixed practice, which includes an explain task. For numbers in the same context, see checking units in a classroom calculation.
For a teacher to rework your own explanations, see online one-to-one Civil Engineering Studies tuition.