The spoon breaks the surface tension of the bubbles, causing them to pop when they start to boil over.
Other people seem to be saying a metal spoon should work just as well (with the added bonus that it won't warp, unlike a wooden spoon), with the only downside that it will be hot to take off. I'm doubtful that a metal spoon would work as well though, because metal does not absorb moisture like wood and also has a smoother surface (i.e. less surface area on a microscopic level), and so it probably wouldn't be as effective in making the bubbles attach and pop. Of course the only way to know for sure would be to do an experiment.
It also depends on the foodstuff and ratio of that food to the volume of water as well. Pot diameter plays a role too, a wider pot provides more room for each bubble and less chance to "climb" one another, plus a wider surface requires more volume of foam to breach the top of the pot.
I'm no chemist, but my observations from cooking and homebrewing, pasta and wort boil over worse than plain water because dissolved starches/sugars/proteins allow the bubbles to have greater surface tension and hold together better. If you cook with more water but the same quantity of food, the bubbles have less surface tension and you can probably avoid the boil over scenario altogether.
For this particular life tip, I would expect a starch-laden foam from cooking pasta to leave a residue on the spoon as the bubbles popped that would eventually let it boil over still. It will buy you some additional time before a mess is made of your stove though.
The spoon breaks the surface tension of the bubbles, causing them to pop when they start to boil over.
Other people seem to be saying a metal spoon should work just as well (with the added bonus that it won't warp, unlike a wooden spoon), with the only downside that it will be hot to take off. I'm doubtful that a metal spoon would work as well though, because metal does not absorb moisture like wood and also has a smoother surface (i.e. less surface area on a microscopic level), and so it probably wouldn't be as effective in making the bubbles attach and pop. Of course the only way to know for sure would be to do an experiment.