How to Write a Functional Behaviour Assessment (FBA) for the NDIS
A functional behaviour assessment stands or falls on one thing: whether you have worked out what the behaviour is for. Get the function right and the support plan almost writes itself. Get it wrong and every strategy that follows is aimed at the wrong target.
Here is how to write an FBA that identifies the function clearly and gives the behaviour support plan something solid to build on. It is written for behaviour support practitioners and allied health clinicians in the Australian NDIS.
Contents
What an FBA is, and who writes it
A functional behaviour assessment works out what a behaviour of concern is communicating, and what it achieves for the person. It is the evidence base for the behaviour support plan that follows. It is written by a behaviour support practitioner the NDIS Quality and Safeguards Commission considers suitable, which includes psychologists, occupational therapists, social workers and other allied health professionals who meet the Commission’s capability expectations.
Describe the behaviours of concern precisely
Vague description is the most common weakness in an FBA. "Aggression" tells the reader nothing they can act on. Describe what actually happens, in observable terms: what the person does, to whom or what, how often, how long it lasts, and how intense it is. A reader who has never met the person should be able to picture the behaviour from your words alone.
Gather ABC data
The engine of an FBA is ABC data: the Antecedent, the Behaviour and the Consequence. For each incident, record what happened immediately before, what the person did, and what happened straight after. Note the setting, the time of day and who was present. Patterns emerge across enough of these that no single incident would show.
Work out the function
Function is the point of the whole assessment. Behaviours of concern usually serve one of a few purposes: to escape or avoid something, to gain access to something or someone, to get sensory input, or to gain attention. Use the ABC patterns to reason toward the most likely function, and say how confident you are and why. This is the finding the plan is built on, so it needs to be reasoned, not asserted.
Link the function to the plan
Every strategy in the behaviour support plan should trace back to the function you identified. If the behaviour is about escape from a demand, the plan changes how demands are made and teaches a safer way to ask for a break. If it is about attention, the plan builds in attention that does not depend on the behaviour. When an FBA and a plan are read together, the logic should be visible from function to strategy.
Common mistakes that weaken an FBA
Three patterns cause the most rework: describing behaviour in labels rather than observable terms, jumping to a function without the ABC data to support it, and recommending strategies that do not match the stated function. Fix all three by writing behaviour first, data second, function third, and only then strategies.
Where Carearoo fits
The clinical thinking is rarely the hard part. The writing is. An FBA and the plan it feeds can run to dozens of structured, repetitive pages that still have to be exactly right. Carearoo drafts the full report from your notes onto your own template in about five minutes, structured from behaviours of concern through ABC data to function and strategies, ready for you to review, edit and sign. Clinical responsibility stays with you.
Frequently asked questions
What is the difference between an FBA and a behaviour support plan?
The FBA works out what a behaviour is communicating and what function it serves. The behaviour support plan uses those findings to set out proactive strategies, skill building and response strategies.
What is ABC data?
A record of the Antecedent (what happened before), the Behaviour, and the Consequence (what happened after), gathered across many incidents so patterns and function become clear.
What are the common functions of behaviour?
Usually escape or avoidance, access to something or someone, sensory input, or attention. The FBA reasons toward the most likely function from the ABC patterns.
How this guide was written
Carearoo researches and drafts its guides with AI assistance, working from the primary sources linked in the text, and a person checks every fact against those sources before it is published. Last checked 27 August 2026.
Have this report drafted in about five minutes
Carearoo drafts the report from your notes on your own Word template. You review and sign off. We'll draft one of your de-identified cases for free so you can judge the output yourself. No cost, no pitch. After that it's $99 a report.