The only time that timmy gets attention is when he misbehaves in a bizarre way. as a result, his abnormal behavior increases in frequency. this is an example of

I believe the answer is: operant conditioning

Operant conditioning refers to a method of learning that could only be done through the use of reward and behaviour. In the example above Timmy learn to favor his misbehaviour because it always resulted in him obtaining the reward that he wants (attention)