The ability to separate the sounds of a word is called “phoneme segmentation”.  It’s a critical skill in both learning to read and write. By six and a half/seven years of age students should be able to tell you the sounds in a word. So, for example, if given the word “cat”, the student should be able to tell you that the sounds in “cat” are /k/ /a/ /t/.  Understanding that words are made up of separate speech sounds is an important foundational skill.  Phoneme segmentation is considered a “phonemic awareness” skill which falls under the broader category of “phonological” skills. Around the end of kindergarten/beginning of first grade we should be directly teaching students to segment words into their