Single pine boards can be pretty easy, especially when they’re dried out, or if they’re using thin wood.
Start stacking the boards up, and the difficulty ramps up pretty quickly and technique is very important, you can smash hard with poor technique and not break the wood. Getting the right distance becomes a key element, as is hitting the target in the right spot.
Switch it up to the plastic rebreakable boards and precision and technique are even more important, as you have to hit on the center line, not be too close (jammed up) and you need decent technique in order to get them to break.
Like kicking shields, heavy bags, etc – its a training tool, and gives students tangible feedback in a way that the other devices don’t. You can push someone holding a kicking shield back with poor technique and a lot of power. You can really rock a heavy back with the same. An instructor can keep harping about “good technique” but the boards can quickly demonstrate the necessity of technique AND power, as well as timing / distance.
Board breaking can be (and often is) just showy stuff to make onlookers Ooh and Aah, but when used properly it is a valid training tool like any other. You would not spend all your time focusing on it, just as you would not spend all your time focusing on any other single training method.
For kids, single wood breaks are at best a confidence builder, and if you’re not using brittle, dry wood, they still require technique. A lot of the people that poo poo breaking have probably not done it, or they break one board as an adult and think there’s nothing to it. Stack up two, three, or more and see how easy it becomes.