It can be hard for some kids to transition from an unvoiced sound such as /p/ to the vowel sound. Vowels are voiced sounds. When I see children with voicing errors, I check the /h/ sound. Many times they omit the /h/ sound before the vowel. Often I see that this has gone unnoticed by their speech therapist. Perhaps the articulation test they used doesn't check initial /h/ or perhaps it's hard to hear. If I can teach them the transition from /h/ to the vowel, then it is so much easier to simply have them say the unvoiced consonant, then the /h/ sound to the vowel. It works! I also stretch out the word really really slowly. They need to hear the transition said slowly. Normal speech rate is too fast. Let them touch your throat and theirs and feel the transition from voiceless to voiced. Another good trick I learned when teaching the Deaf and Hard of Hearing is using the tactile feedback of air on the back of the hand when producing /h/. Let them hold one hand in front of your mouth and the other hand in front of theirs.
You can also follow this link to an activity I created that you can use to contrast initial vowel words with initial /h/ words.
http://www.quia.com/jg/1284061.html
