Children have different learning styles. Developmental psychologist Howard Gardner defines six different intelligences/learning styles. 

Linguistic intelligence: sensitivity to spoken and written language. 

Logical-mathematical intelligence: the capacity to analyze problems logically, carry out mathematical operations, and investigate issues scientifically.  

Musical intelligence: skill in the performance, composition, and appreciation of musical patterns.  

Bodily-Spatial intelligence: the potential to recognize and use the patterns of wide space and more confined areas. 

Interpersonal intelligence: the capacity to understand the intentions, motivations and desires of other people.  

Intrapersonal intelligence: the capacity to understand oneself, to appreciate one’s feelings, fears and motivations.

If your child is learning his letters, pay attention to how he learns best. If he is musical, you can sing him the sounds of the alphabet while pointing to the letters. If he is very social, you can have a dialogue about the letters. If he is bodily-kinesthetic, you can have him trace/walk giant letters on the sidewalk or trace the letters in shaving cream. If he is logical-mathematical, have him put pieces of a letter together to form the whole letter.Try multiple methods of teaching your child. Cognitive neuroscientist Bruce Perry says that the more varied the ways that information is inputted into the brain, the stronger the neuronal connection for that piece of information.