To make your classroom a child-friendly environment, you need child-sized furniture. Children need to be comfortable to learn, so provide tables and chairs at their level. When setting up activities on a shelf, make sure the highest shelf is still accessible to your smallest student. A child needs the confidence to be able to independently reach the materials, without risk of dropping from it being too high. Anything that the children are to be able to access should be within their reach. Having to ask a teacher to reach something eliminates that factor of independence.
Provide comfortable floor areas. If carpet is not an option, use a large area rug. Comfortable pillows or cushioned chairs in the reading corner encourage children to nestle with a book. Work rugs help to define the child's workspace on the floor, allowing for organization of materials as well as reassurance of ownership over that work at that time.
If sinks and toilets are too tall for a child to comfortably reach, provide a small stool or steps to enable the child to safely reach them.
Use the furniture in the classroom to provide natural walkways. Check the flow of the classroom. Do you have an elongated "runway"? Children who cannot yet control their bodies will feel invited to take off in flight. Put a plant or a small shelf or table in the path to curb those fast movements. Observe the flow of the children and tweak as necessary. You are trying to encourage careful movements.
Children should have access to the entire spectrum of the Montessori curriculum. How you allow children to explore it is going to depend on your own interpretation of the philosophy and training. Some believe that a child can take out any activity and the teacher needs to scale the lesson back appropriately. Others do not allow children to touch a work until he or she has had a lesson on it.
Montessori materials should make up the bulk of your works. Some areas, such as language, require a lot of teacher-created materials. Be sure that your creations fall into Montessori guidelines and that you can justify their presence in the room.
Aim for as much wood and natural items as you can find. Do not fear glass. Children need to learn to be careful with materials. Plastic simply bounces and does not break. No lesson is learned when that drops. But a fragile piece of glass can shatter. The child will use more care in the future. Wood is much more attractive than brightly colored plastic. Children will be more likely to be drawn to it.
Decorating the classroom
Use a soft palette when painting the classroom walls. Avoid hanging lots of brightly items. If you choose to decorate the walls, use artwork that is hung at the children's level. If you display the children's artwork, make sure it is matted on a background and rotate it. I sometimes like to add an educational poster, depending on our topics of study. For example, while doing the human body, I put up a poster of a child with the basic parts labeled. It hung on the classroom door, at the children's eye level. When they went into the hallway to do their full body tracings, they could label their body according to the poster.
Use plants for decoration. They also serve a practical purpose of teaching children how to care for them and for providing oxygen and purifying the air. They are absolutely beautiful and make for cozy surroundings.
Avoid cluttered areas. I am extremely guilty of allowing my own things to clutter and to start to take over other areas of the classroom. I make a concentrated effort to reduce that on a regular basis. If children have clutter in their area, they will not take care of their things.
Remember that less is more.
The ideal outdoor environment has plenty of space for children to run free and to safely exercise those gross motor skills. They should also have areas where they can care for plants and animals. Allow them to explore, to find natural items such as seeds. Take walks. Embrace the outdoors and bring it inside as much as possible. Conversely, do not fear taking materials outside, as well. Think back to those original photographs of Maria working in her Children's House. Many children are stretched out in the garden with a rug and work.
Remember that the classroom is not about you. It is about them. Give them ownership of the classroom. Teach them to maintain it by helping you clean and straighten. You are guiding them in how to care for it.