My DS7 was tested at 4 and at 6. The first time the neuro-psych used legos as a motivator and allowed my son to play with them during breaks. This backfired as my son LOVES legos and rushed to finish. He still scored high enough to be identified as gifted but the dr thinks his score may actually be 20-30 points higher. When he retested at 6 his score did rise a good bit but that examiner also used toys during break time and left them out in his view during the test.
Not sure if this helps you. I just know that when my son is retested I will make sure there are no toys around.
And yes - a good breakfast & lots of rest are key. I would add if your child appears to be getting ill - I'd reschedule. My son had a raging ear infection for his second test. Of course I did not realize this until he started to complain an hour or so after the test.
Good luck!! :-)
