The best way to get your son to take out the trash without being told would be to reward your son on a schedule of reinforcement at first, then change to a schedule.

continuous schedule and switch later to partial schedule (variable ratio)

Explanation: reinforcement schedule can be said to be guidlines or rules that govern how, when a behavior should be expressed. It determines the rate of occurence of a target behavior, how it will happen, strengthens it and even when it will continue or stop.

There are 2 types of reinforcement schedule. Which is continuous and partial schedule. The continuous reinforcement schedule tend to use the positive reinforcement strategy. It rewards for a particular behavior is on a continuous basis. Everytime a target behavior is expressed, the person or animal is rewards. The partial reinforcement schedule is of four type and the best for this kind of behavior after switching from continuous reinforcement schedule is the variable ratio schedule. Here a behavior is rewarded variably. The person does not know when the reward will come and so he continues to portray that behavior expected of him or her. It's the best type of schedule when switching from continuous reinforcement schedule.