Behavioral Skills Training (BST) is a training package that utilizes instructions, modeling, rehearsal, and feedback in order to teach a new skill. Typically training is implemented not for some fixed time, but rather to some predetermined criterion. For example, a trainee may be said to have acquired a skill when they have emitted correct responses on 90% of three consecutive training sessions. Although these four components are common there are many procedural variations in how researchers and practitioners apply them. For example, modeling might be done live, in role play, or through video-modeling. Feedback might be given immediately or delayed, graphically or verbally, or in combinations.