ByIn order to encouraginge the zero liminatioccurrence of the target behaviour, BST students will allow Sam to Sengam’ge in his preferred engagcting vinty, social interaction behaviours, when Samhe shows zerno ratesign of of task avoidance behaviour. According to the duration record of Sam’s task avoidance behaviour, Sam demonstrates tahisk avoidance behaviour for 3three minutes per each individual work timnterval. The longest task avoidance behaviour lasts for 14 minutes and 52 seconds, and the shortest one lasts for 23 seconds (see appendix E). FIn order to determininge the first/initial length of reinforcement, 3three minutes onf working time will be set. Then, the omission period will be increased by 3three minutes per day. The goal is to extend the duration of time toSam works on the task during the entire individual working period. As a part of DRO procedure, 3three minutes of preferred activity time will be allowed when Sam successfully works on a task during the set interval.