Montessorians often use the language of, "Freedom with limits," to describe the open ended choice enjoyed by children in these environments. You'll just as often hear, "Follow the child," to describe the child-directed nature of those choices. So why do so many classrooms require children to receive formal lessons with the materials before they're permitted to remove them from the shelf?
The Montessori materials are carefully designed, elegant activities intended to support the child in mastering a single concept at a time. Each mastered concept contributes to the complexity of more advanced materials, and, in turn, to the complexity of the child's understanding of the concepts. For example, a learner building the full Trinomial Equation, laid out prism by prism along a complicated chart with labels for a^3, b^3, c^3, a^2b and so on, must have first mastered all the smaller concepts within the equation. Before a learner can demonstrate mastery of the Trinomial Equation, the learner needs to understand what a cube is, how to label each edge of a prism, the concept of addition, the gross motor capacity to carry the cube, the fine motor capacity to move the prisms, and the order and concentration required to organize all these pieces at once. A learner who would like to offer freshly cut carrots to the class must first know how to carry a tray, how to wash vegetables, how to control a vegetable peeler, how to manage the compost, how to serve and how to clean up. Each of those lessons, in turn, has its own composite parts: how to move chairs, how to walk around the classroom, how to replace the lid on a bucket, how to wet a sponge, how to wash one's hands, and so on.
As adults, we often presume these activities to be easier than they are (in the classroom and at home!) But the protection of the isolated concept is essential to the functioning of the Montessori classroom. By offering lessons that isolate single concepts, teachers are able to better assess a child's development, understanding quickly what part of the lesson the child may be struggling with and identifying what may need another presentation. Because the sequence of isolated concepts builds upon earlier mastery, a learner who "jumps ahead" to a more complicated activity may quickly find that jump left them in over their head, overwhelmed by the multiple challenges and frustrated by their inability to manage them all. Especially in the critical window Montessorians call, "the Absorbent Mind," when every experience teaches the child about the world and their ability to contribute to it, we provide challenges that require for concentration and allow for manageable struggle, but we try not to set the child up for failure.
So, what does a Montessori teacher do with a child who wants to use a material that is too advanced for that moment in the child's development? In some classrooms, you might see teachers who engage a child in observing those lessons, reminding them gently that, "One day, you will have this lesson, too!" You might see teachers creatively engage the child and the material for a lesson that is in the child's ability, for example, "I can see you noticing the beautiful glass beads of the thousand chain. Come, and I'll give you a lesson in bead polishing." These alternative lessons satisfy the child's desire to touch and engage with the beautiful materials on the shelves, but allow the teacher to circle back when the child is developmentally ready for the concept to suggest, "Come and I'll show you a new lesson with the Five Chain." Some classrooms may have more hands-off boundaries, where you'll notice teachers saying, "This is such a beautiful material. Let's look at it together on the shelf," engaging the child in a conversation about the lesson without yet taking it to a mat or table. These can be tricky conversations: a child who is attracted to a beautiful lesson on the shelf is acting exactly the way the materials are designed to inspire. We offer beautiful materials because we want to draw the child's attention and care for them. But a teacher can often satisfy the desire to touch a lesson that's conceptually too advanced by offering a child other engagements instead, including advanced, wonder-filled conversations about what it is about these lessons that makes them so appealing to begin with.
And truth be told, some of the magic of the Montessori classroom is lost without these limits. When children can handle any materials they choose, with or without a presentation from the teacher, we see them offering less care to the materials. The wonder that comes with having observed other children at work and having worked toward the lesson is lost. It becomes much more difficult to entice a child to a lesson that does emphasize the concept to be learned if a child thinks he or she has "already done that work." Children are aware of their own growth as well, and the joyful expressions that teachers notice throughout the classroom when a child has mastered something with which they have been struggling require that struggle first. The limits allow for the wide range of development present in any one classroom to be met, support the child in developing persistence through challenges, and, most importantly, preserve the elegance of the isolate concept, allowing children to master those concepts more authentically, when the time is right.