Well, give him time! It's all new to him. The trailing bike does sound like a good idea, because it will give him a chance to see how much fun it is to ride!

The 4-year-old I know just moves her feet back and forth which means she's constantly putting on the brake. She hasn't figured out how to go in circles yet! She's also not highly motivated, so they aren't pushing it, figuring she may be more interested in another month or two.