I like to have parents sit in on my evaluations. I find that most children are not distracted by their parents at all. Very rarely I will have to ask a parent not to coach if we are doing a standardized test, but this is very uncommon. Having parents sit in on evaluations allows them to see what is being done and it enables them to be better advocates for their children. Parents who have seen occupational therapy evaluations are better able to discuss a child's needs at a CSE or CPSE meeting. Also, having a parent 'right there' allows me to interact with them as contextual behavioral issues come up and it also allows me to observe the nature of the parent-child interactions.
The one exception to this rule is that I generally don't like to have parents present in the room if I am doing the SIPT. I can't tell you how many parents have fallen asleep while watching this evaluation - it must be the most boring thing in the world to watch. So, if I am giving the SIPT I usually tell the parents to go out for a while and I bring them into the evaluation close to the end.
What are your experiences with having parents observe and participate in the evaluation process? Let us know!