Some children are raised in homes where English is not spoken, or where non-standard dialects of English are spoken. Likewise, some children suffer auditory trauma or ear infections that affect their ability to hear speech. Any child who is not consistently exposed to English phonology may have difficulty perceiving the subtle differences between English phonemes.
Note that when some children produce words that sound similar, they may not be able to articulate distinctly enough for others to hear the distinction. Difficulty with articulation does not imply difficulty with perception.
Children who are not able to hear the difference between similar-sounding words like grow and glow will be confused when these words appear in context, and their comprehension skills will suffer dramatically.
Young children sometimes have problems articulating certain sounds, but they can usually distinguish between the sounds within a word when somebody else speaks. In other words, they do not have a problem with phonology; they have a problem with articulation.
To test whether or not a child has simply made a speech error, try parroting the word back to the child in the form of a question. If the child says, “I want to go pray outside,” ask the child, “You want to go pray outside?” The child with normal phonologic skills will repeat herself, emphasizing the indistinct word, in an attempt to make you understand what she is trying to say.
Play the “same or different” game. Generate pairs of words that are either identical or that differ in a subtle way. Examples of similar sounding words are slow and snow, or black and back. Say them out loud and ask the child if they are the same or different. Children should rarely miss the ones that are different. If the child misses more than just a few, please consult with the speech therapist at your school, or advise parents to take the child to a pediatrician or an audiologist.