“TH” is a sound that many children have trouble producing, but it is a very easy sound to teach. There are actually two TH sounds. One is voiceless, as in the word, “bath.” The other is voiced, as in the word, “that.” The voiceless TH is usually mastered by age 5 or 6, but the voiced TH may still be mispronounced by many children until age 7.
TH is produced by protruding the tongue slightly between the front teeth and blowing. The voiced TH is produced the same way, but uses the voice instead of the breath.
Demonstrate TH using a mirror. Instruct the child to “bite your tongue and blow.”
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.
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.
Have your child practice the TH in isolation until it is easy for him. Then have him try it at the beginning of words, such as thing, thick, thunder, this, or that.
My book, Super Star Ch, J, and Th contains many other helps, practice activities, picture cards, and games to help you teach your child the TH sound.