First, care should be taken to consider whether this strategy is helping to maintain problem behavior. If your son is attempting to terminate an ongoing activity by engaging in problem behavior, the strategy might be associated with release from that activity plus access to a desired activity. This is a dangerous combination in that it results in strengthening the probability of problem behavior while engaging in aversive activities. Consider having a functional behavioral assessment conducted. Further, it is always preferable to be able to anticipate activities that have a higher probability of association with problem behavior. Consider delivering the relaxing activity contingent on engagement rather than waiting until the learner becomes upset.