I was a karate practitioner and instructor in my youth. Board breaking is really, really easy. The key is the boards designed for breaking are cut in their weakest orientation. Wood is incredibly strong going with the fibers, even a pine board is very hard to break long ways using a sledge hammer. However, if it's cut on its short axis, it's incredibly easy to break. Most people, even children don't need any guidance beyond, "punch through the board" to be successful. Breaking boards is more mental than physical. If a student is struggling or a novice, the person holding the board can hold their hands a little wider to make it easier to break.
Concrete is more difficult, but there's still a trick to it. The blocks you use for breaking have a bit of flex to them, but are also extremely brittle. So just getting it to flex just a small amount will cause them to break in half. That's also why you place spacers between stacks of bricks or wood. You're leveraging the flex of the material to break it, and stacking them without spacers makes too rigid to break.
Concrete is more difficult, but there's still a trick to it. The blocks you use for breaking have a bit of flex to them, but are also extremely brittle. So just getting it to flex just a small amount will cause them to break in half. That's also why you place spacers between stacks of bricks or wood. You're leveraging the flex of the material to break it, and stacking them without spacers makes too rigid to break.
In short, this stuff is 90% magic trick.