Educate yourself about the Montessori Method. Many resources are available via the Internet and your local library that cover the Montessori schools. Most Montessori schools also have background references available to interested parents. Seek opinions from parents who had children in Montessori schools, especially if the children were the same age as your child is now.
Be honest about your child's learning style. If the child learns best through physically manipulating objects (tactile or kinesthetic learning style), then he is likely to learn well in a Montessori environment. If the child is naturally curious and self-motivated, the program may fit her better than a structured classroom environment.
Consider your child's special needs. Montessori students have freedom of movement and are allowed to talk quietly amongst themselves while working. This is not a good fit for some children with sensory integration issues. Also, some children with Attention Deficit Hyperactivity Disorder (ADHD) have difficulty staying on task because there are so many options to distract them.
Visit the school. Most Montessori classrooms have windows from which you can observe classes while standing in the hallway. Watch how the children interact during a work cycle, and determine if you would like this environment for your child.
Inquire about the cost. Private Montessori schools typically have expensive tuition costs. You may have to pay for materials that are free in public schools. Some public school systems offer free public Montessori schools as part of their magnet school system, so find out if a free option is available in your area.