To put it simply, forest schools take the learning outside: children do a lot of the activities they might do in regular childcare or an early education environment, but they do them all outdoors. The open-ended play and learning happens outside, where kids can learn by counting mushrooms, observing plants, or lifting up rocks just to see what's living underneath them.
The areas of focus for forest schools are ones that most parents would agree are valuable. Kids are encouraged, through interaction with nature, to learn and develop socially; to be physically active and emotionally fit; to develop self-confidence; to learn respect for their neighborhoods and environments; and to enjoy nature in safe and age-appropriate ways.
Having the ability to explore freely outside — within a controlled environment, and under the supervision of educational professionals — lets kids learn at their own pace and explore as they are comfortable.
Children allowed to explore freely, in ever-changing natural environments, are going to have to get creative with play and use their problem-solving skills to deal with weather, natural barriers, and other factors of the outdoors.
Children get the opportunity to not only observe nature with their eyes but to really engage with it, with all their senses. Sensory play is important for childhood brain development and helps children develop and make sense of their relationships to the world around them.