youpi,
Well, I think I know what the problem is. Declan is plain cheeky! As feedbacked by the teacher, he knows what he's being asked, but will just refuse to do it or purposely do something else.
Eg: When we arrive at home in the evening when the sky is clearly dark, we will ask Declan to say good evening to the helper. He will look at the sky, think for a little while, and then say good morning with a cheeky smile.
HOW???