In January I visited the preschool (where my son was enrolled more than a few years ago) to observe and talk to teachers. This school is located in a dense urban neighborhood and serves a diverse group of children.
The outdoor space is a hotbed of activity. One of the favorite winter pastimes, according to teachers, is playing with rain: pouring, scooping, carrying water, 'cooking' with wood chips, making mud, watering plants.

Below are some comments from teachers. I've included their 'wish lists' as well. You never know.

on outdoor space

• Outdoor space is critical.
• Have a door directly to the outside so that children can go freely in & out; doors should be easy to open. Bigger kids can go up and down stairs to go outside.
• Wish list: more land, huge garden, animals, kids' bike shed for afternoon rides, dirt mounds, outdoor amphitheater.
  

on child-centeredness

• Independent exploration is important.
• Things should be child-sized; not too many high walls; let children see and survey the entire room.
• Children want to squeeze into small spaces.
• Children should be able to open windows as long as it is safe.
• Let the kids build their own world. Avoid Disney-fication.

on teacher's needs

• Everything should be mobile so that the teacher can arrange the space as needed.
• You always need more space than you think, particularly outside.
• Storage for each classroom is ideal; it is nice to be able to see what you plan to use the next day.
• Music spaces need soundproofing. In general, acoustic dampening is very important.
• Wish list: display/presentation space for the whole school. For example, weekly, a language teacher could leave out materials and objects.
  

2. nail on some bark

3. grow some plants