Montessori begins introducing sounds to three year olds. Knowing the names of the letters isn't as important as knowing the sound each letter makes. It's also common practice, in Montessori, to introduce children to lowercase letters first rather than uppercase letters. This is because most of the letters in books, that children will begin to read, are lowercase. It's easier for them to make connections. This is opposite of what most public schools teach.
In my classroom, in addition to introducing Sandpaper Letters individually to children, children are introduced to a new sound at circle each Tuesday. A small, very low table is set up with the Sandpaper Letter of the "sound of the week", at least 4 small objects that each begin with the same initial sound and a book featuring the sound of the week in the title. In the picture above, the sound /p/ was accompanied by objects such as pizza, pig, pumpkin and pear and the book title included the word peace for /p/. Since the work will be out for the week to be done by children independently, the objects help the youngest children in the room remember what the letter sounds like without having to ask an adult. Once they look at the objects, assuming they know what the objects are called, they can recall the sound. The sound of the week table also includes a Sand tray so that children can "write" the letter in the sand as that helps with muscle memory and they learn to form the letters. Giving children, this age, paper and pencils is not a great idea as most three year olds are not yet ready to hold a pencil and correcting a bad pencil grip is harder than teaching it correctly the first time.
The 26 Sandpaper Letters take us through most of the school year since we feature one a week. Then I start introducing phonograms. Children love the Sandpaper Letters and they are a beautiful Montessori material.