FBA vs Functional Analysis in Schools: Decision Rules

A student hits, runs, or throws, and the IEP team says, "We need an FBA." Someone asks, "Do we need a functional analysis?" Someone else asks whether the RBT can just run it. This post gives school BCBAs plain answers and six decision rules for how much assessment a student needs.

What is the difference between FBA and FA?

A functional behavior assessment (FBA) is the whole process of finding out when and why a behavior happens. A functional analysis (FA) is one method inside that process. The analyst arranges antecedents and consequences on purpose and measures whether behavior changes across them (Cooper et al., 2020, p. 632; Iwata et al., 1982/1994).

Every FA is part of an FBA. A school FBA does not have to include one.

For the full FBA process, start with the Functional Behavior Assessment guide. To turn a confirmed hypothesis into a plan, see From FBA to BIP and Function-Based Behavior Intervention Plans. This post covers one narrower question: do you test a working hypothesis or move to intervention?

What are the three types of functional assessment?

Cooper et al. (2020) group FBA methods into three types: indirect assessment, descriptive assessment, and functional (experimental) analysis. They sit on a continuum. Indirect methods are easiest to use, and functional analysis gives the most precise information (p. 631).

Indirect assessment

Indirect methods are interviews, checklists, rating scales, and questionnaires completed by people who know the student (Cooper et al., 2020, p. 631).

The limit: these reports cannot show that the reported events maintain the behavior. Cooper et al. (2020) caution that closed-ended instruments such as the MAS and QABF have been repeatedly shown to be unreliable and of questionable validity for identifying function (p. 641). Hanley (2012) recommends open-ended interviews as a way to design a functional analysis. Hanley also advises that treatment should typically not be designed from interview results alone.

Descriptive assessment

Descriptive methods are direct observation under naturally occurring conditions: ABC continuous recording, ABC narrative recording, and scatterplots (Cooper et al., 2020, p. 635). They show what comes before and after the behavior in real routines, how often, and when.

The limit: a consequence that often follows the behavior may not be the one maintaining it. Descriptive assessments tend to give false positives for attention, because adults often attend to severe behavior whether or not attention is the reinforcer. They can give false negatives for escape, because adults may stop presenting the demands that trigger the behavior (Cooper et al., 2020, p. 635).

Thompson and Iwata (2007) compared descriptive and functional analyses for 12 participants. In only 3 of the 12 cases was problem behavior maintained by the consequence observed most often in the descriptive analysis. ABC data is still worth collecting, as a source of hypotheses to test.

Functional analysis

In a functional analysis, each test condition presents a motivating operation and a potential source of reinforcement for the behavior. A control condition provides the reinforcer freely with no demands (Cooper et al., 2020, p. 632). The team then compares levels of behavior across conditions.

Cooper et al. (2020) describe it as the only FBA method that allows practitioners to confirm hypotheses about those relations (p. 631). Hanley et al. (2003) reviewed the functional analysis literature, and Hanley (2012) counts 277 articles in that review.

The limit: an analysis can miss idiosyncratic variables that its conditions do not represent. The process can also temporarily increase the behavior (Cooper et al., 2020, p. 633).

Cooper et al. (2020) also say: "FAs should be flexible and individualized" (p. 632). There is no single standard FA with four mandatory conditions.

A decision tree: do we need a functional analysis?

The decision tree in text

1. Start with a written working hypothesis from your indirect and descriptive data.
2. Do interviews and observations point to the same function across several routines? If they conflict, test before you plan, and choose an analysis format.
3. If they agree, is the behavior dangerous to the student or others? If yes, write the safety plan first. If the school cannot staff it safely, use a precursor or latency-based analysis, or refer. Do not run it without trained staff and a safe setting.
4. If the behavior is not dangerous, did a function-based plan already fail when it was run with good fidelity? If yes, test the hypothesis and choose an analysis format.
5. If no plan has failed, move to a function-based plan and treat the plan as the test. Write the hypothesis, collect baseline, choose the measure, and set a review date.
6. Choosing a format: trial-based FA when the teacher can step away for short trials during normal instruction. Latency-based FA, or an analysis of precursors, when the behavior is too severe to repeat many times. IISCA when several reinforcers seem to arrive together and an open-ended interview is possible. Brief FA when time is very short and a consultant is available.

Which should be done first, an FBA or a BIP?

The FBA comes first, and the behavior intervention plan (BIP) is built from it. Cooper et al. (2020) describe FBA as a four-step process (p. 641):

1. Gather information with indirect and descriptive assessment.
2. Form hypotheses.
3. Test hypotheses using functional analysis.
4. Develop intervention options based on the function of the behavior.

The plan comes last. The IDEA discipline regulation follows the same order. When the team finds that conduct was a manifestation of the disability, the IEP team must conduct an FBA and implement a behavioral intervention plan. The exception is when an FBA was done before the behavior that led to the change of placement (34 C.F.R. § 300.530(f)(1)).

If a plan already exists, the team reviews and modifies it as necessary (34 C.F.R. § 300.530(f)(1)). Your state and district set the procedures and timelines for requests outside discipline, so check them before you promise a family a date. If you are writing the plan now, see Behavior Intervention Plan Examples.

Can an RBT do a functional analysis?

An RBT can take part in a functional analysis under close supervision. In practice, the supervising BCBA owns the decision to run one, the design, and the interpretation. Three BACB documents support that answer:

• The RBT Test Content Outline (3rd ed.) applies to RBT exams beginning in 2026. Task B.3 reads "Participate in components of functional assessment procedures (e.g., descriptive assessment, functional analysis)" (BACB, 2023).
• The RBT Handbook says RBTs practice "under the direction and close supervision of an RBT Supervisor and/or an RBT Requirements Coordinator" (BACB, 2026). Those supervisors "are responsible for all work RBTs perform" (BACB, 2026).
• The RBT Ethics Code (2.0) repeats the supervision requirement (BACB, 2021).

Cooper et al. (2020) say trained practitioners should plan and run analyses (p. 634). So the practical split is simple:

• The supervising BCBA decides whether to run an FA, chooses the format, writes the safety plan, trains the implementers, and reads the graph.
• An RBT or a trained paraprofessional can collect data. They can run sessions when the BCBA has trained and observed them. Paraprofessionals acted as therapists in some of the school analyses Mueller et al. (2011) summarized.

The same answer applies to "Can an RBT do an FBA?" An RBT can take part in parts of it, such as descriptive observation. The BCBA owns the assessment.

Trial-based functional analysis

What it is. A series of short trials placed inside normal classroom activities. Each trial has two parts, each lasting 1 minute. In the first, the teacher presents the motivating operation and the contingency (the test condition). In the second, the student has continuous access to the reinforcer (the control condition).

Trials happen when the conditions naturally occur, such as free play for tangible tests and instruction for escape tests (Cooper et al., 2020, p. 634).

When a school BCBA would pick it. Pick it when you need a test but a full session-based analysis does not fit the school day. It suits a student who stays in the classroom and a teacher who can step away for a minute at a time.

Cooper et al. (2020) describe an analyst who chose a trial-based FA with the teacher running the conditions. She worried about the time a traditional FA would take and the teacher's ability to run it with fidelity (pp. 644-646).

Staffing and safety. Running conditions in the classroom can disrupt routines and may require additional supervision so that other students are covered (Cooper et al., 2020, p. 634). In the case, each of four conditions ran 8 times for 1 minute during regular instruction (Cooper et al., 2020, p. 645). Write down who covers the class, who records, and what ends a trial early.

The evidence. Bloom et al. (2011) exposed 10 students referred for problem behavior to trial-based analyses and compared the results with standard functional analyses. The two corresponded in 6 of the 10 cases and partly corresponded in a seventh. The authors concluded that a trial-based analysis may be a viable method when the resources for a standard analysis are not available. Cooper et al. (2020) add a limit: exposure in each trial may be too brief (p. 634).

Latency-based functional analysis

What it is. Each session ends as soon as the problem behavior occurs. The measure is the time from the start of the motivating operation to the first occurrence of the behavior (Cooper et al., 2020, p. 634). Shorter latency in a condition points to that condition as the likely function (Cooper et al., 2020, p. 646).

When a school BCBA would pick it. Pick it when the behavior is so severe that repeated occurrences are not acceptable (Cooper et al., 2020, p. 634). If even one occurrence is too risky, Cooper et al. describe a related option: analyze a precursor, a behavior that reliably comes before the target behavior. Their example is growling before aggression (p. 634). Hanley (2012) also describes precursor analysis.

Staffing and safety. Cooper et al. (2020) give an example with a student who eloped. The analyst started a stopwatch when each condition began, stopped it at the first elopement, and assigned additional therapists to every exit (p. 646).

In a school, that means extra adults, a blocking plan, a time limit, and covered exits. Cooper et al. warn that protective equipment can invalidate results and that widely accepted safety standards still need more research (pp. 634-635). Hanley (2012) advises talking with medical professionals when the behavior is self-injury.

The evidence. Thomason-Sassi et al. (2011) ran three experiments and found an inverse relation between response rate and latency. They concluded that latency may be useful when repeated occurrences of behavior are undesirable or impractical to arrange. Only one exposure to the contingency occurs per session (Cooper et al., 2020, p. 634). Only one of 42 school studies in Nesselrode et al. (2022) used a latency-based analysis, so the school evidence is thin.

What is an IISCA and how many conditions does it have?

What it is. An interview-informed synthesized contingency analysis (IISCA) uses an open-ended interview to build the analysis. In the test condition, several contingencies are delivered together when the problem behavior occurs, for example attention and escape. In the control condition, those same reinforcers are delivered continuously and for free (Cooper et al., 2020, p. 634).

So an IISCA has two conditions: one test and one control. They alternate rapidly (Practical Functional Assessment, 2015).

When a school BCBA would pick it. Cooper et al. (2020) say it may be useful when problem behavior does not show up in typical FA conditions and more than one contingency may maintain it (p. 634). In their example, a child's behavior did not appear in separate attention and tangible conditions but appeared clearly when both were delivered together.

That effect appeared when the child's mother delivered the contingencies and not when the behavior analyst did. So train and observe the adult who will run it.

Staffing and safety. The test condition still evokes problem behavior. Plan the setting, the adults, the blocking procedures, and the criterion for stopping. Practice with a coach before running one with a student.

The evidence. Hanley et al. (2014) described an assessment and treatment process for 3 children with autism. After an 8- to 14-week outpatient clinic consultation, no problem behavior was observed in the clinic or at home. Jessel et al. (2016) reported 30 IISCAs that averaged 25 minutes of analysis.

The limited research comparing the IISCA with standard functional analysis is conflicting, so its utility is as yet unclear (p. 634). The sources cited here include no study of the IISCA in a public school classroom. Treat it as an option to consider with training and consultation.

Practical functional assessment

What it is. Practical functional assessment (PFA) is the name Hanley's group uses for a whole process. It has three parts: an open-ended interview, an IISCA, and treatment built from what the analysis showed (Hanley & Fiani, n.d.).

When a school BCBA would pick it. Pick it when you want assessment to lead straight into teaching replacement skills, and you have coaching or consultation to learn the process. It is a larger commitment than a trial-based analysis, because it covers assessment and treatment. Plan the same safeguards as any analysis, and train every adult who will carry out the treatment.

The evidence. Hanley and Fiani (n.d.) state that peer-reviewed research has shown the IISCA to be quick, safe, and reliable. That statement comes from the group that developed the process. Cooper et al. (2020) call the independent comparisons conflicting (p. 634). Read both before you decide.

Decision rules for school teams

These rules are a framework for team discussion, not a professional standard. Hanley (2012) reviews common obstacles to running analyses and ways to overcome them. Use the rules to make your reasoning explicit and documented, then apply clinical judgment.

Rule 1: Clear, consistent hypothesis and low risk: test it through the intervention

Move to a function-based plan without a formal functional analysis when all of these are true:

• Interview and observation data point to the same function.
• The pattern is consistent across several observations and routines.
• The behavior is not dangerous to the student or others.
• No prior function-based plan for this behavior has failed.

Treat the plan as the test. Write the hypothesis down, define the measure, collect baseline, and set a review date. If the behavior does not change when the plan is run with fidelity, the hypothesis may be wrong. This is a weaker test than an FA, because many things change at once.

One comparison supports not defaulting to an FA every time. Call et al. (2024) compared FBAs that included a functional analysis (26) with FBAs that did not (31) for 57 young children with autism spectrum disorder. The two kinds of FBA showed modest correspondence, and every participant who completed functional communication training had a successful outcome regardless of the type of FBA. The study did not involve school classrooms, so use it as a reason to ask the question, not as a rule.

Rule 2: Conflicting hypotheses: test before you plan

When interviews and observations point to different functions, or different staff describe different patterns, a stronger test is usually worth considering. Thompson and Iwata (2007) show how often the most frequent consequence in descriptive data can mislead. A plan built on the wrong function can make the behavior worse. Cooper et al. (2020) give the example of replacing playtime with intensive instruction for a student whose tantrums escape a task, which may exacerbate the behavior (pp. 630-631).

Rule 3: Severe or dangerous behavior: consider an analysis, with safety planning first

It is tempting to rule out a functional analysis whenever behavior is dangerous. Hanley (2012) argues the reverse: the more dangerous the behavior, the more important it is to determine its function accurately. The central risk question is whether the student would be at greater risk in the analysis than during a typical school day. Precursor analyses, latency-based measures, short sessions, soft materials, and clear criteria for ending sessions can reduce risk (Hanley, 2012; Cooper et al., 2020, pp. 634-635).

If safety equipment or enough trained staff are not available, the setting may not be safe for an analysis (Cooper et al., 2020, p. 633). Then document why, and consider a precursor analysis or a referral.

Rule 4: A function-based plan already failed: reexamine the hypothesis

If a plan built on the current hypothesis was run with fidelity and did not work, the hypothesis is the first thing to question. Check fidelity before blaming the function. If fidelity was adequate, an experimental test is a reasonable next step. Writing a new plan on the same evidence is not.

Rule 5: Low-rate behavior: do not assume an analysis is impossible

Low-rate behavior is hard for every method. Cooper et al. (2020) list infrequent behavior as a limitation of functional analysis (p. 633). Hanley (2012) notes that motivating operations are arranged repeatedly in an analysis, so differentiated results can be obtained even for reportedly low-rate behavior. Sessions can be extended or timed to when the behavior is likely.

Rule 6: The result would not change the plan: skip it

If every plausible function would lead to the same support, a functional analysis adds cost without changing the decision. Assess to the depth the decision requires.

Before any functional analysis in a school

Even when the rules point toward an analysis, put these in place first:

• Consent and authorization. Follow district policy for informed consent, and confirm the analysis is covered by the assessment plan the team agreed to.
• Staffing. Running sessions in a classroom may require additional staff to supervise other students (Cooper et al., 2020, p. 634).
• Safety plan. Define the criterion for ending sessions, the blocking procedures, and what happens if the behavior escalates (Cooper et al., 2020, pp. 634-635). Involve medical professionals when self-injury is a concern (Hanley, 2012).
• District policy. Your district may have specific rules about assessment procedures, restraint, and crisis response. Check them before you write the protocol.

Closing thought

Whether you run more functional analyses or fewer, choose on purpose, write down why, and revisit the choice when the data say the hypothesis was wrong.

If you work as a BCBA in schools, the School BCBA Systems Transformation Program helps you build these assessment systems with a cohort of peers.

Frequently asked questions

References

Authority of school personnel, 34 C.F.R. § 300.530 (2026). https://www.ecfr.gov/current/title-34/section-300.530

Behavior Analyst Certification Board. (2021). RBT ethics code (2.0). https://www.bacb.com/wp-content/uploads/2022/01/RBT-Ethics-Code-240830-a.pdf

Behavior Analyst Certification Board. (2023). RBT test content outline (3rd ed.). https://www.bacb.com/wp-content/rbt-outline-3rdEd/

Behavior Analyst Certification Board. (2026). Registered behavior technician handbook. https://www.bacb.com/wp-content/uploads/2025/08/RBTHandbook_260529-2-a.pdf

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Cooper, J. O., Heron, T. E., & Heward, W. L. (2020). Applied behavior analysis (3rd ed.). Pearson.

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Hanley, G. P., & Fiani, T. (n.d.). Practical functional assessment. https://practicalfunctionalassessment.com/

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Hanley, G. P., Jin, C. S., Vanselow, N. R., & Hanratty, L. A. (2014). Producing meaningful improvements in problem behavior of children with autism via synthesized analyses and treatments. Journal of Applied Behavior Analysis, 47(1), 16-36. https://doi.org/10.1002/jaba.106

Iwata, B. A., Dorsey, M. F., Slifer, K. J., Bauman, K. E., & Richman, G. S. (1994). Toward a functional analysis of self-injury. Journal of Applied Behavior Analysis, 27(2), 197-209. https://doi.org/10.1901/jaba.1994.27-197 (Reprinted from Analysis and Intervention in Developmental Disabilities, 2(1), 3-20, 1982, https://doi.org/10.1016/0270-4684(82)90003-9)

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Nesselrode, R., Falcomata, T. S., Hills, L., & Erhard, P. (2022). Functional analysis in public school settings: A systematic review of the literature. Behavior Analysis in Practice, 15(3), 958-970. https://doi.org/10.1007/s40617-022-00679-8

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Thomason-Sassi, J. L., Iwata, B. A., Neidert, P. L., & Roscoe, E. M. (2011). Response latency as an index of response strength during functional analyses of problem behavior. Journal of Applied Behavior Analysis, 44(1), 51-67. https://doi.org/10.1901/jaba.2011.44-51

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