TH is a very easy sound to teach because it is easy to demonstrate to the child. TH is produced by protruding the tongue slightly between the front teeth and blowing. The voiced TH is produced the same way, but using the voice instead of airflow.
1.Demonstrate TH using a mirror. Instruct the child to “bite your tongue and blow.”
2.If the child substitutes F or V for TH, draw his attention to the use of the tongue and teeth to make the sound. The teeth and lip should not make contact. Practice “f-th-f-th” to contrast the two sounds. If necessary, gently push the lower lip out of the way.
3.To teach the voiced TH, instruct the child to imitate the voiceless TH and to “turn his voice on.” It may be taught by having him say “zzzz,” then gradually move
his tongue forward to between the teeth.