The Montessori baric tablets help a child learn to discriminate slight differences of weight. The lightest colored wood tablets are the lightest, the medium wood color tablets are the middle weight and the darkest wood tablets are the heaviest in weight. I just introduced this lesson when my daughter turned 4.
Although I have read variations of this lesson, this is how I was instructed to present: The first lesson with the tablets is without the blindfold and using only the lightest and the heaviest tablets. The adult sits across from the child and demonstrates how to hold her arms up, elbows bent and palms out, fingertips slightly bent. The adult places one of the lightest tablets on the child's fingertips and says, "this is light." The adult places one of the heaviest tablets on the other fingertips and says, "this is heavy." Varying the light and heavy order, the adult continues with all the tablets. Next, the adult places a light and heavy tablet simultaneously on the child's fingertips, pauses, and says "show me heavy" "show me light" (At this time, if the child is not able to give the correct response the adult should not continue but smile and thank the child for the lesson and try again at a later date.) If the correct response is given the adult continues for the remaining tablets and the child makes a stack of heavy and of light tablets. The child can check his/her correctness visually because of the different tones of wood. This concludes the first lesson.
After the child is familiar with the activity, a blindfold can be added. The child can then use the two sets again, making a heavy and light pile. After using these two sets successfully, the middle weight can be introduced. This is done using light and medium and later medium and heavy. Lastly, the child can work with all three sets sorting into three piles.
A parent could make a similar activity at home using available objects to introduce heavy and light to their child. Although a homemade lesson might not be as controlled as using the Montessori tablets, heavy and light could be introduced with a variety of objects (rocks and feathers, balls of clay, I even thought of making my own with bean bags) and would accomplish the goal of discriminating different weights and heightening the child's awareness of weights in the environment.