Each letter or digraph is framed in with dashed lines. Each dashed line represents part of the Montessori three-period lesson.
Upon the initial introduction of a letter, you would trace over the left dashed line as a way to remind yourself that this letter has already been formally introduced.
Once your child is able to recognize and identify each letter or digraph, you would then trace the top dashed line. For example, if you’re able to ask your child to pick up the letter that makes the sound /a/ or, on a different occasion, to give you the letter that makes the sound /a/ and they are able to successfully identify the correct letter repeatedly, this indicates proficiency with the second part of the three-period lesson.
When your child demonstrates mastery with a letter or digraph and is easily able to tell you the sound it makes, you would then trace over the right dashed line, thereby completing the box around the letter or digraph.
Of course this doesn’t mean that once a box has been completed you ignore it. Repeated exposure to letters already known helps boost a child’s confidence, serves to further solidify their understanding, and, by urging a child to continue to trace over the letter, helps to prepare the hand for writing.