When making the /d/ sound, the tip of your tongue should be placed on the front part of the roof of your mouth, right behind your upper teeth. Your tongue should also be tense, and your vocal chords should be voiced or vibrating when you make this sound. The sound is released as a puff of air when your tongue is lowered from its position.
When making the /th/ sound, the tip of the tongue sticks out briefly a tiny bit and is pressed against the upper front teeth, so that it vibrates slightly as the air is released around the sides
of your tongue and teeth. Sometimes the vocal chords are voiced when making this sound.
Read these words to your student(s) and have them repeat.
For more pronunciation exercises, come in to pick up a copy of Pronunciation Fun! (Free for IC teachers and students.)