Children often improve their target sound production when words are easy using the smartpalate, but as words get more complex it's harder to accurately produce the words.
Longer syllable words can often cause a child to compromise the clarity of the word as he trys to complete the word. He might leave off unstressed syllables, or reduce the vowels, or blur the parts together.
Here is one fun example of how to use objects to support syllable production while watching the palatometer display to point out to the child that he can still make proper tongue-palate contact and sound. You could also record the child talking and play it back for him to review.