Grouping living things with keys
Biology · Key Stage 2 · The School
Group by what you can see
Classification starts with features anyone can check: does it have a backbone, six legs, wings, feathers, scales? Grouping by colour or by "nice" fails immediately because two people disagree. A good grouping feature gives the same answer whoever applies it, which is why keys ask about structure and not about opinion.
How a branching key works
A BRANCHING KEY asks a yes/no question that splits the group in two, then asks again of each half, until only one organism is left. "Does it have a backbone?" then "Does it have feathers?" and so on. Each question must have exactly two answers and no overlap, or the reader reaches a fork where both branches seem right.
Building one
Start with all your organisms and find the feature that splits them most evenly — that keeps the key short. Write the question so it cannot be answered "sort of". Then repeat on each half. Test it by handing it to someone else with one organism: if they arrive at the wrong name, the fault is in your question, not in them.
Build a key for a spider, a beetle, a woodlouse and a worm. Step 1: does it have legs? No → worm. Yes → step 2. Step 2: more than eight legs? Yes → woodlouse. No → step 3. Step 3: exactly eight legs? Yes → spider. No → beetle. Now run all four through it. All four come out right and each step splits the group in two, with nothing left over — that is the test a key has to pass.