Discrete trial and ABA methods are often confused, but they are not identical. Discrete trial is a teaching strategy used within the umbrella that is ABA. It is a method of instruction that works to shape behavior through the use of repetition and cause and effect learning. Discrete trial is a "scaffolding" or "chaining" method that builds one skill on top of another. Complex tasks are broken down into small steps and each step is mastered in turn across a series of trials.
Tasks differ in their complexity. Basic tasks such as being able to sit quietly for an extended period are prerequisites for other, more complex tasks such as working with a computer program. Being able to speak the phrase, "hello, how are you" is a prerequisite for more complex social communication tasks such as greeting someone (which may also involve making eye contact, and paying attention to what the other person has to say). Discrete trial learning methods recognize this hierarchy of tasks, and attempts to teach more basic prerequisite type tasks first.
A typical starting task for discrete trials work is to be able to simply sit at a workstation. The directive, "come sit" is often one of the first goals for discrete trial students. When students can sit and attend to tasks without having a tantrum or becoming aggressive, they are ready to take on more complex tasks, including social and communicative tasks. Communication skills teaching frequently starts with basic skills like learning to make appropriate eye contact, and progresses towards more advanced communication skills, including object labeling and use of sign language to convey needs.
Discrete trial methods are designed to increase the likelihood that student children will act in desirable ways. It is not designed to decrease their tendancy to act in undesired ways. Children are motivated to act in desired ways through the application of reinforcement techniques. Positive reinforcement occurs when behavior is rewarded, such as by providing a desired treat. In order to be effective, rewards must be presented immediately, and be concrete in nature. Rewards that are intangible, or which are delivered after a delay may not be associated with desired behaviors and may appear to children to have simply been granted for no reason. Discrete trial methods never use punishment methods (which involve adding something negative and aversive to the children's environment). However, negative reinforcement methods, which involve rewarding children when they stop doing something undesirable, are fair game.
Apart from shaping student children's behavior towards the acquisition of social and communicative skills, discrete trial methods also teach children about cause and effect. Students learn that they are expected to respond to trials, and that every response they make will have a consequence (e.g., they will either be rewarded for their response or they will not). Therapists are ultimately interested in getting children to pay attention to task learning and in developing their ability to respond appropriately to communication. Letters, numbers and object labeling skills are thus acquired as a byproduct of discrete trials training. Because communicative skills are basic and fundamental and must be present before more complex social skills can be taught, they are taught early on in the process.