Take a real object, say its name slowly, and point to the written letter that matches its first sound.
You know the sounds. Now match them to the written letters. Pick a toy, say its name, and find the letter it starts with.
This time, you are matching to the letter shape, not just the sound.
Mastery looks like: They can take a real object, isolate its first sound, and correctly point to the matching written letter.
Common stumbles: Matching to the wrong but similar-looking letter; forgetting to say the word slowly before searching for the letter.