is the Echo Smartpen by Livescribe.
It isn't cheap at around £170, and you have to add the cost of the special digipen paper which must be used. The paper is necessary whichever digipen you buy, because these pens work by reading a dot grid that's pre-printed on the paper.
Your son will also need Optical Character Recognition software on his laptop, so the pen's data can be converted to text files. That's not too expensive, but it all adds up.