Functional Behavior Assessment (FBA): Methods, Steps and an Example

Two students in the same classroom throw their pencils. One does it because the teacher rushes over every time. The other does it because the teacher sends them to the hallway, and the hallway has no fractions. Same behavior, opposite reasons, and the response that fixes one makes the other worse.

A functional behavior assessment is how you tell those two students apart. Most pages about FBAs are written for parents heading into an IEP meeting. This one is for the people who run them: RBTs collecting the data, special education staff, students in an ABA program and future BCBAs. It covers the three FBA methods, the steps from first interview to summary statement, a worked example, when the law requires an FBA, who is allowed to conduct one, and how it shows up on the RBT and BCBA exams.

What Is a Functional Behavior Assessment?

A functional behavior assessment (FBA) is a process for finding out why a behavior happens. It looks at what comes before the behavior, what the behavior looks like, and what follows it, and it ends with a best explanation of what the behavior gets the person or helps them avoid. That explanation is the behavior's function.

The function matters more than the behavior's form. Hitting, crying, running away and tearing up a worksheet can all serve the same purpose, and one behavior can serve different purposes for different people. Behavior analysts usually sort functions into four groups: attention, escape, access to tangibles, and automatic (sensory) reinforcement. Our guide to the four functions of behavior covers each one with examples.

Schools tend to say "functional behavioral assessment," which is also the term in federal special education rules. ABA clinics often say "functional assessment." All three names mean the same process. The output feeds straight into a behavior intervention plan (BIP): the FBA works out why, and the BIP decides what to do about it.

The Three Types of FBA Methods

An FBA isn't one test. It's a set of methods that get more precise and more demanding as you go down the list. Most FBAs use more than one.

Indirect Assessment

Indirect methods ask other people about the behavior instead of watching it. A structured interview covers what the behavior looks like, how often it happens, when it's most and least likely, what people usually do in response, and what the person can already do instead. Rating scales such as the Questions About Behavioral Function (QABF), the Motivation Assessment Scale (MAS) and the Functional Analysis Screening Tool (FAST) turn those answers into scores for each possible function.

Indirect tools are fast and cheap, and they are the right place to start. They are a poor place to stop. A parent and a teacher can give confident, opposite answers about the same child, and both can be wrong. Treat the result as a hypothesis to check, not a finding.

Descriptive Assessment (ABC Data)

Descriptive assessment is direct observation in the real setting, without changing anything. The usual format is ABC data: for each episode, the observer writes down the Antecedent (what happened just before), the Behavior (what the person did, described in observable terms) and the Consequence (what happened just after). Some teams use a narrative log, others a checklist with the likely antecedents and consequences pre-printed so staff can tick boxes quickly.

Scatterplots are a common companion. They mark when the behavior happens across the day and the week, which can reveal that it clusters around a particular class, staff member or time.

Descriptive data is real behavior in the real world, which makes it valuable. Its weakness is that it shows correlation. If a teacher reprimands a student after almost every outburst, the data will show attention following the behavior, but that doesn't prove the attention is what keeps it going. The outburst might be about escaping the task, with the reprimand just along for the ride.

Functional Analysis

A functional analysis tests the hypotheses directly. The evaluator runs short, repeated sessions under different conditions and graphs how often the behavior happens in each one. A typical set looks like this:

• Attention. The adult is busy and gives brief attention (such as a mild reprimand) only after the behavior.
• Escape (demand). The adult presents tasks and removes them briefly after the behavior.
• Tangible. A preferred item is removed and given back briefly after the behavior.
• Alone or ignore. No social consequences at all, which tests for automatic reinforcement.
• Play (control). Free access to attention and preferred items, no demands. The behavior should be low here.

If the behavior is consistently high in one condition and low in the control, that condition points to the function. The method traces to Iwata and colleagues' 1982 study of self-injury, which exposed nine participants to brief, repeated conditions that varied play materials, demands and social attention. In six of the nine, self-injury was consistently higher in one specific condition (Iwata et al., reprinted 1994). A later review by Hanley, Iwata and McCord called functional analysis "a hallmark of contemporary approaches to behavioral assessment" (2003).

Functional analysis is the only FBA method that shows cause and effect. It also deliberately sets up the conditions for problem behavior, so it needs a trained designer, staff who can run each condition exactly, clear rules for ending a session, and a safety plan when the behavior is dangerous.

What FBA Methods Do Behavior Analysts Actually Use?

In textbooks, functional analysis is the gold standard. In practice it's the exception. Researchers at the University of the Pacific sent a survey to 12,431 BACB-certified behavior analysts and got 724 back. Most respondents regularly used FBA methods, especially descriptive assessment, and many rated descriptive assessment and functional analysis as the most useful. But fewer than half reported using functional analyses in practice, and a majority said they "never" or "almost never" used one to identify the function of behavior (Oliver, Pratt and Normand, 2015).

That gap is worth knowing about on the job. Most FBAs you'll see in schools and clinics are built on interviews and ABC data. That's often enough to write a good plan, but it means the function is a hypothesis, and the plan's data is what confirms or overturns it.

How to Do a Functional Behavior Assessment, Step by Step

Forms differ between districts and agencies, but a complete FBA moves through the same steps.

1. Define the target behavior. Write an operational definition: what it looks like, when an episode starts and stops, and what doesn't count. "Aggressive" isn't a definition. "Hits, kicks or pushes another person with enough force to move them" is. If there are several behaviors, prioritize by danger and by how much each one gets in the way.
2. Review records. Prior FBAs and BIPs, the IEP or treatment plan, discipline records, medical history, medications and recent changes at home or school. This is BCBA task F.1: identifying relevant sources of information in records at the outset of the case.
3. Interview and use rating scales. Talk to the people who see the behavior most, and to the person themselves when they can take part. Ask about setting events too: sleep, hunger, illness, a change in routine.
4. Observe and collect ABC data. Across several sessions, settings and times of day, including times when the behavior doesn't happen. Measure a baseline (frequency, duration or intensity) at the same time.
5. Look for the pattern. Group the ABC records by antecedent and by consequence. Which triggers show up again and again? Which consequence follows most episodes?
6. Test the hypothesis if needed. When the indirect and descriptive data disagree, the behavior is severe, or a plan based on them has failed, a functional analysis can settle it.
7. Write the summary statement. One sentence per function: when [antecedent], [person] does [behavior], to get or avoid [consequence]. Add setting events that make it more likely.
8. Hand off to the behavior plan. The summary statement goes into the BIP, and every strategy in the plan has to match it.

A Worked FBA Example

Here's a compressed example of the descriptive part of an FBA. The student is fictional and the data is illustrative.

Target behavior. Maya, grade 2, puts her head down on the desk and refuses to respond, counted from when her head touches the desk until it's lifted for 10 seconds.

The pattern across a week of rows like these: the head-down episodes happen when Maya is asked to read aloud, not during work in general (she finishes the spelling test, which only asks her to write). Most episodes end with the reading demand removed. The interview adds that her reading fluency is well below grade level and she has said reading out loud is "embarrassing."

Summary statement. When Maya is asked to read aloud in front of peers, she puts her head down and stops responding, to avoid reading aloud. It's more likely on days with a new or longer passage.

Notice the 10:40 row. There, the consequence was attention and help, which could suggest an attention function. One row doesn't make a pattern, but it's the kind of mixed evidence that leads a team to keep collecting data or to run a brief functional analysis. If the summary statement had been "attention," the plan would have done the wrong things: more check-ins from the aide, and still no help with reading.

With the escape hypothesis, the behavior plan follows: practice the passage privately before reading it to a partner, a way to ask for help or a shorter turn, reinforcement for reading attempts, and reading instruction for the skill gap that makes the task so aversive.

When Is an FBA Required?

In schools, federal special education law names the FBA directly in its discipline rules for students with disabilities.

• After a disciplinary change of placement found to be a manifestation of the disability. The IEP team must "conduct a functional behavioral assessment, unless the LEA had conducted a functional behavioral assessment before the behavior that resulted in the change of placement occurred, and implement a behavioral intervention plan" (34 CFR 300.530(f)). A change of placement means a removal of more than 10 consecutive school days, or a pattern of shorter removals that totals more than 10 school days in a school year (300.536).
• When a student is removed for disciplinary reasons. The student must "receive, as appropriate, a functional behavioral assessment, and behavioral intervention services and modifications" designed to keep the behavior from happening again (300.530(d)(1)(ii)).

Those are minimums. Federal rules separately require the IEP team to consider positive behavioral interventions and supports for any student whose behavior impedes learning (34 CFR 300.324(a)(2)(i)), and an FBA is the usual first step. Many states and districts go further, requiring an FBA before certain interventions or after a set number of incidents, so check your state's rules. Outside schools, an FBA is a standard part of ABA treatment whenever a client has a behavior to reduce.

Who Can Conduct an FBA?

In ABA clinics and home programs, a BCBA designs and interprets the FBA. The 6th edition BCBA Test Content Outline lists "Design and evaluate descriptive assessments" (F.5) and "Design and evaluate functional analyses" (F.6), and then interpreting the data to choose goals and procedures (F.8). A BCaBA may help under a BCBA's supervision.

RBTs participate. The RBT outline's task B.3 is to "Participate in components of functional assessment procedures (e.g., descriptive assessment, functional analysis)." In practice that means collecting ABC and baseline data, running test conditions exactly as the BCBA wrote them, and reporting anything that might affect the results. An RBT doesn't decide what the function is. If you want to see where this fits in the job, read what an RBT does.

In schools, the IEP team is responsible, and the FBA is usually led by a school psychologist, a behavior specialist, a special education teacher with behavior training, or a district BCBA. Teachers and aides collect much of the observation data. Exactly who is qualified to conduct an FBA is set by each state and district, not by federal law.

Common FBA Mistakes

• Stopping at the interview. A rating scale result written up as the function, with no observation behind it.
• A vague target. "Noncompliance" or "meltdowns" can't be counted consistently, so the data won't mean anything.
• Observing only when the behavior happens. Without the quiet times, you can't see which conditions make the difference. Maya's spelling test was as informative as her reading.
• Too few observations. Three ABC entries from one afternoon will show a pattern whether or not there is one.
• Missing setting events. Sleep, pain, medication changes and trouble at home can make every trigger worse. They belong in the summary statement.
• Assuming one function. Some behaviors serve more than one. A plan that treats only one will help only partly.
• An FBA that never reaches the plan. If the BIP's strategies don't follow from the summary statement, the assessment was wasted.

FBAs on the RBT and BCBA Exams

On the RBT exam, FBA content sits in Behavior Assessment, which has 3 tasks and carries 8 of the 75 scored questions (11%). Task B.3 is the one about functional assessment. Expect scenario questions: you're running a condition in a functional analysis, or you're taking ABC data, and you pick the response that follows the protocol or the detail that belongs in your notes. Questions about identifying functions sit in Behavior Reduction as task D.1.

On the BCBA exam, Behavior Assessment (Domain F) has 8 tasks and 23 scored questions, about 13% of the exam, which makes it the most question-dense domain per task. F.5 and F.6 are the FBA tasks. Expect to read a descriptive data set or a multielement FA graph and pick the function, or to pick the right assessment for a situation. Our BCBA task list guide lists every task with its weight.

Frequently Asked Questions

Sources

1. 34 CFR 300.530 - Authority of school personnel (FBA and behavioral intervention plan)
2. 34 CFR 300.536 - Change of placement because of disciplinary removals
3. 34 CFR 300.324 - Development, review, and revision of IEP (special factors)
4. BACB, RBT Test Content Outline (3rd ed.) - task B.3, Behavior Assessment domain weight
5. BACB, BCBA Test Content Outline (6th ed.) - tasks F.1, F.5, F.6, F.8
6. Iwata, Dorsey, Slifer, Bauman and Richman, Toward a functional analysis of self-injury (1982; reprinted in JABA, 1994)
7. Hanley, Iwata and McCord, Functional analysis of problem behavior: a review (JABA, 2003)
8. Oliver, Pratt and Normand, A survey of functional behavior assessment methods used by behavior analysts in practice (JABA, 2015)