In the toddler years this is adequately assessed during the cleanup, and telephone tasks. I am seeking similar age-appropriate tasks for 4- to 6-year olds.
I think mainly the interview is used but maybe this will interest you - here, on page 6 there are some methods described which include observation in laboratory:
Thank you Ania. I thought the clean up task was not age-appropriate for 5- to 6-year olds. But structured problem-solving tasks that increase in difficulty sound good.