1. The first method is simply to ask your child (assuming he is verbal) what are his favorite things or activities in the world!
2. Another technique is to talk with the child and during the conversation topics that he enjoys may come up.
3. Observation of the child is another method. The therapist or parent can spend some time just observing the child to see what he enjoys doing! If he plays with Legos everytime he has free time this may be a reinforcer for him. The Premack Principle in Psychology states in common words that the behavior that is frequently performed can be used to reinforcer lower frequency behavior. Therefore, observation to see what the child does most frequently during the day.
4. Another method are to administer an inventory or checklist which are commonly used by therapist to determine what items are reinforcing to a particular child. This can be done with the parent and or the child reporting what the want typically as reinforcers and the person records the responses on a checklist.
5. Reinforcer sampling first used with mental patients inspired by Nathan Azrin is another method used to determine what items are reinforcing. This techique utilizes a sample for the child (Ayllon, T. & Azrin, N. H. (1968). Reinforcer sampling: a technique for increasing the behavior of mental patients. Journal of Applied Behavior Analysis, 1, 13-20).