As children learn the sounds of the alphabet and how to blend those sounds into words, they should also be taught to form the letters correctly and to segment sounds in words and write letters (graphemes) for those sounds. This helps them understand that spelling is the reverse process of reading. When they are taught this way, children link the letters to their corresponding sounds from the very beginning.
Here are pictures of children learning to form letters and spelling words with sounds they have already learned. These activities are from the Dandelion Launchers workbooks which complement the Dandelion Launchers reading books.