It's about being able to learn, make decisions and risk-take in a safe way.
A trained Forest School Leader will follow the 6 principles of Forest School. It's about being holistic about the child; many children struggle to learn, especially when younger, in the rigid classroom environment. It's learner-centered, so children can feel they can explore or follow the activities they want. They learn about risk (for example use of tools, fires, climbing a high tree) in a safe way, but develop skills that they can take out into the world.
Many schools don't really do "proper" Forest School. I've seen some classes have just 6 weeks of outdoor learning in a whole year, whereas it should be regular. I've also seen classes all being told to follow certain activities in the woods, even once having to play a phonics game rather than going and exploring of their own free choice.
It's not for everyone, but I'm a trained Leader. I've taught Year 5 pupils who, in the classroom, struggle to follow authority and be verbally aggressive, yet in the woods they have really come to life and been amazing pupils who respond so positively to everything. It just shows that unfortunately the classroom is not for everyone. I wish I could have taught those pupils every day outside in the woods.