Lesson 1.2 — The ABC Model

The three-term contingency

The ABC model is the analytical foundation of everything in ABA. Every behavior occurs in a context: something happens before it, the behavior occurs, and then something happens after it. Understanding this sequence is how behavior analysts identify why a behavior is happening and how to change it.

A — Antecedent

The event, stimulus, or condition that occurs immediately before the behavior. Antecedents set the stage for behavior; they don’t cause it directly, but they increase or decrease the likelihood that a behavior will occur.

Examples of antecedents:

• A teacher says, “Time to clean up” (before a tantrum)
• A therapist presents a math worksheet (before the client pushes it away)
• A peer sits next to the client (before the client hits)

B — Behavior

The observable, measurable action performed by the individual. This must be described in specific, objective terms, not inferred emotional states.

Examples:

• The client throws the worksheet on the floor (not “the client got frustrated”)
• The client says “no” and walks away (not “the client was uncooperative”)
• The client hits a peer with an open hand three times

C — Consequence

The event that follows the behavior. Consequences are critical because they determine whether a behavior will increase or decrease in the future. A consequence that increases behavior is a reinforcer. A consequence that decreases behavior is a punisher.

Examples of consequences:

• The teacher removes the math worksheet (consequence: escape provided)
• The RBT says “great job!” and gives the client a sticker (consequence: social + tangible reinforcement)
• The peer moves away (consequence: negative reinforcement of hitting)

Why the ABC matters for the exam

The exam frequently presents scenarios and asks you to identify the antecedent, behavior, or consequence, or to identify what function the consequence serves. Read every scenario carefully and ask:

1. What happened just before the behavior? → Antecedent
2. What did the person actually do? → Behavior
3. What happened right after? → Consequence
4. Did the consequence increase or decrease the behavior? → Reinforcement or punishment

Common exam trap: Students sometimes confuse the antecedent and the motivating operation (MO). The antecedent is the immediate trigger in the environment. The MO is a broader condition that changes how much the person values a consequence (like hunger increasing the value of food). These are related but distinct, and you will encounter both on the exam.

Reading an ABC correctly: worked example

A client is doing a puzzle with an RBT. The RBT’s phone buzzes and the RBT looks away. The client immediately begins banging the puzzle pieces on the table. The RBT looks back and says, “Hey, stop that.” The client smiles and continues banging.

• Antecedent: The RBT looks away (attention is removed)
• Behavior: Client bangs puzzle pieces on the table
• Consequence: The RBT looks back and verbally addresses the client (attention is provided)
• Function: Attention — the behavior was reinforced by gaining the RBT’s attention

This sequence tells us the behavior is maintained by attention. The intervention would need to address the antecedent (keep attention on the client) and the consequence (withhold attention for banging, provide attention for appropriate behavior).

Quiz 1.2 — The ABC Model

15 questions · No time limit · Scenario-heavy