What is reinforcement in ABA?
Reinforcement is anything that follows a behavior and makes that behavior more likely to happen again, and it is the core mechanism ABA uses to build new skills.
Reinforcement is defined by its effect, not by intent. If a consequence increases the behavior it follows, it reinforced that behavior; if the behavior doesn't increase, it wasn't a reinforcer no matter how rewarding it was meant to be.
It takes two forms. Positive reinforcement adds something after the behavior - praise, access to a preferred item, a turn at a favorite activity. Negative reinforcement removes something aversive, such as ending a demand once the learner asks for a break.
What works is individual and shifts over time, so teams assess preferences regularly and vary what they use. Plans also work to move from contrived reinforcers toward the natural consequences a skill will meet outside of session.