We have noticed the same thing with our daughter who just turned three. She is very selective about what she will do. If she is not interested she will start talking about something unrelated or she will leave. I worry how this would affect any formal testing we might have done in the future. I asked her to count to 20 for me yesterday and she got to about 12 and then trailed off and ran away to do something else. Then later that day she did 7 pages of addition in a new book she had picked out. Our local school wants us to have her screened, but I am worried that she might not cooperate.