I've been re-reading L&T03, which is perhaps the more comprehensive language training study on ToM. The conclusion is fairly clear -- language helps, no language, no help. Sentence complements are useful, so are simply sentences that pointed out what the child failed to perceive. L&T argued for a discourse-based interpretation.
As much as I like this paper, the question in my mind is their ToM measure -- an appearance-reality test. They were asked 3 questions
1. What do you think is inside (the box before its content is revealed)
2. What did you think was in the box when you first saw the box (after the surprise content was revealed)
3. What your friend X will say in the box when s/he sees the box for the first time
Notice the shift of tense and aspect in the three cases. I wonder if 3.5 year old (German speaking) children will get these.
Also in the sentential complement test II (Hale & Tager-Flusberg, 2003), the child was asked the following question:
"What did the girl say she was cutting?"
which has a deep structure: "the girl say-ed she is-ed cutting WHAT".
This would be easily confused with
"what did the girl .... was cutting?" --> "what did the girl cut" or "what was the girl cutting?"
Did anybody tried to do a shadowing test, and ask the child to repeat the question after certain delays? I suspect what they perceived (or memorized) is quite different the input.
Or, instead of a production, do a forced choice comprehension test.
The point is -- the appearance-reality task hinges on the correct interpretation of a tricky sentence, which involves shifting tense and aspect of a past event. Is this ToM or language comprehension? Or from the Whorfian point of view, does this matter? It's all linguistically constructed.