So how does it work? Well, as the name implies, there are three parts to the lesson. The first period is the naming lesson in which the child is told the names of objects (one by one, in isolation). The second period is the recognition stage in which the child is asked to remember a specific object. Finally, the third period is when the child recalls the name of a specific object.
That's a very brief description of the three period lesson. I haven't gone into a long explanation about how to present the lesson because there are lots of examples all over the internet. (Here's a very good description if you want to learn more.) However, the best way to see a three period lesson is to ask your child's teacher - not the assistant - to give you one. If she doesn't know how to do a three period lesson......I would question the authenticity of her Montessori training.
The importance of the Three period lesson can't be underestimated. This tool can be used anywhere. In the classroom we use it to introduce letter sounds, number values and symbols, continent names, plants and animals, but it is not limited just to the classroom. It can also be used in the playground, in the kitchen, at music lessons, even at the super market. It can even be used to introduce object names in a second language. There is no limit to how this lesson can be used because, under the right circumstances, there is no limit to the amount of information a child between the ages of 3 and 6 is capable of absorbing.
Nor does the three period lesson stop when a child enters a Montessori elementary classroom. Like so many other concepts, the lesson becomes more abstract as the older child gradually moves away from the concrete. For example, a botany lesson might begin with the examination of a flower and the naming of its various parts (naming). The second period (recognition) happens when a child works with the three part cards of the flower. ( Each card has a picture and corresponding label. Working with this material, the child gradually memorizes the name for each part.) Finally , in the third period, the child challenges himself by using the definition cards to identify the correct picture and label.
The real beauty of the three period lesson is that it allows Montessori teachers to meet each child exactly where they are. In other words, the technique allows the children as much time as they need to learn each new concept - some children will absorb a concept quickly and only need the lesson once or twice while other children may want to be given the lesson many times until they are confident enough to move on.