Well, it depends....
If your child attends Montessori school outside of the home, it is better not to buy duplicates of the equipment that he or she uses in school. The presentation you give will be different from that given in the classroom and, besides, your child will have plenty of time to use it at school.
If you are homeschooling, you absolutely need the equipment! A few pieces of age-appropriate equipment plus a one or two pieces of material that will be at your child's next level will provide a basic platform for creating a full range of material at home. Mix in DIY equipment and you are done. If you have a talent for DIY, then you need to purchase almost no equipment.
What is hard to make? The Golden Bead and other bead material for the math section can be tricky and the Movable Alphabet can be tedious to make in cut-out form, but almost everything else can be made fairly easily. Visit Montessori for Everyone for some great Adobe PDF material.
Learn more about making equipment and using it with our Montessori Teaching Album for Infants and Toddlers.
Adventures in Autism
12 years ago