Trials to criterion

The measure counts opportunities before mastery

A trial is one defined opportunity to respond under stated conditions. The criterion identifies the performance required before the skill is considered mastered for that phase. The count includes eligible trials from the declared starting point through the trial that completes the mastery rule.

Suppose a rule requires four correct independent responses among five consecutive trials across two probes. The count continues until both probes meet the rule. Reporting only the final five trials hides the teaching exposure that came earlier.

Define criterion before teaching begins

A criterion should name:

• the response and acceptable forms
• independence and prompt rules
• correct and incorrect outcomes
• eligible opportunity and exclusion rules
• required performance level and window
• number of sessions, probes, people, or settings
• treatment of errors, breaks, missed trials, and procedure changes

Choose the rule for the skill and decision. Ninety percent across one session, three consecutive independent demonstrations, and a task completed safely across two settings answer different questions.

Count valid trials consistently

Start from the first eligible opportunity after baseline or the declared teaching phase begins. Include errors and prompted responses when the protocol counts them. An invalid opportunity stays documented with its reason rather than disappearing silently.

Do not count a trial against the learner when materials are unavailable, the communication system is inaccessible, the instructor changes the plan mid-opportunity, or the person withdraws from a nonemergency activity. If preparing materials is a scored staff step, record that implementation error separately.

Mark retraining, pauses, target revisions, and instructor changes. Combining versions can make one trials-to-criterion number uninterpretable.

A fictional vocational routine

Kai is a fictional young adult who selects a goal of using speech or AAC to request a missing supply during a volunteer sorting task. With Kai, the team defines an eligible trial as a naturally needed item that a partner can provide or discuss. Independence means a recognizable message before any prompt.

The mastery rule is four independent requests in five trials across two probes with two partners. Kai meets the first probe on trials 9 through 13 and the second on trials 14 through 18. Trials to criterion is 18.

The final probe contains four independent responses of five, or 80%. That percentage alone cannot show the 18 opportunities used to reach the rule. The team separately records partner response, prompt use, chosen breaks, and whether Kai finds the routine useful.

Use it as an efficiency measure with caution

Fewer trials to criterion may indicate faster acquisition under the observed arrangement. It can also reflect an easier target, looser criterion, stronger starting skill, more intensive prompting, different reinforcement, or more favorable opportunities.

Compare teaching procedures only when targets, mastery rules, trial definitions, exposure, and learner conditions are sufficiently similar. Report sessions and elapsed days beside trial count because 20 trials in one day differ from 20 spread across a month.

Cost per mastered target may add staff time, materials, supervision, and burden. Efficiency remains subordinate to safety, choice, access, clinical appropriateness, and durable benefit.

Sparse measurement can change apparent mastery

A study of skill acquisition across six children and 100 training sets found that continuous and discontinuous measurement could produce different acquisition and maintenance pictures under those procedures. The full paper supports treating measurement frequency as part of the method.

Another reanalysis involving 11 children found that first-trial data could indicate mastery earlier than fuller trial data. These studies do not establish that one schedule is always correct. They show why the observation plan and mastery calculation must be explicit.

Mastery needs later checks

Trials to criterion ends at the first qualifying point. Continue with separately defined maintenance, generalization, fluency, preference, and social-validity checks when they matter. A skill may meet criterion during structured teaching and remain unavailable in another setting or with another partner.

If later performance falls below the rule, retain the original trials-to-criterion value and document the new phase. Rewriting the old count erases useful history.

Protect communication and choice

Keep AAC, interpreters, mobility and sensory supports, breaks, food, water, bathroom access, prescribed care, and emergency help available. Explain the goal and process accessibly. Obtain required consent and assent when applicable and respond to withdrawal or distress.

The BACB BCBA Test Content Outline, Sixth Edition identifies trials to criterion as an efficiency measure and covers measurement, reliability, validity, and skill-acquisition evaluation. It provides exam content, not an individualized mastery rule.