A: It is not a realistic goal for four years olds to recognize or to write the letters of the alphabet. Children differ a great deal in their skills in this area: occasionally a child of four is able to read simple words but often normal children still struggle to write individual letters correctly at six. Academic skills are not really applicable to a four year old--a child of four should be in a setting that encourages age-appropriate social interactions with other children, imagination, and engagement with language through talking, explaining, and listening. Communication starts with people first, and only later with paper and pencil. Rushing this process doesn't work.
If you have concerns about your son's development, I would encourage you to consult with your pediatrician or family doctor to make sure that there is no reason to worry. What you describe here, however, does not sound like a problem.
Elizabeth Berger MD