Is he obsessive/compulsive?  Maybe these are small clues?

What works with some children, is a timeframe or schedule.  For example,  if you visit the park let him know that you are only spending 20 minutes there.  Give him a 5 minute warning prior to leaving the park.

Difficulty making transitions is a symptom of some brain-based conditions. ADD/ADHD for instance has this characteristic. It is called a "soft neurological sign." However, people without any other health conditions can have these soft neurological signs. Having trouble with fine motor movements in one example. Reversing numbers or letters is another example. There are numerous minor brain glitches and most people have one or more of them. Once we understand this, we can be more sympathetic to a child with a transition problem. It's not just that he's "bad" or "defiant." Rather, he really has trouble disconnecting from the activity that he is doing. Sometimes nutritional support can make a difference to brain functioning. You could try adding EFA's to his diet (essential fatty acids). Some companies make EFA supplements especially for kids - check with your local pharmacist of health food store or naturopath. EFA's are found in foods such as salmon and flaxseed but for therapeutic purposes you will probably need a supplement. You can also experiment with the Bach Flower called Walnut. It is specific to helping people make transitions of all kinds Sometimes people experience improvement within the first few doses and other times it may take weeks before you begin to notice a change. You can consult a Bach Flower Practitioner for instructions or ask a health practitioner. There are numerous on-line resources for Bach Flowers as well. On the behavioral level, you can help your son by giving him warnings that a transition will be required. Give him 5 minutes advance notice, followed by one more "2 minute" warning and then the final request. Be generous with praise when he does make an efficient transition ("Wow - you finished off so quickly and came right away - that was so speedy of you!"). Keep up a program of positive attention for a month. After that, you can begin to use gentle negative consequences for not coming right after that third notice (even people with transition difficulties can learn to pull away from what they're doing). Three warnings, praise and negative consequences can all work together along with brain support to help your son negotiate transitions more easily.  Sarah Chana