In the gifted community... it's generally recommend to AVOID testing FOR AS LONG AS POSSIBLE unless it's needed for admission into x, y, z, or for special services.
Here's a good 100+ hour reading on the subject http://www.hoagiesgifted.org/
When you CAN'T avoid it, it's also really important to make sure they're being evaluated by a gifted kid specialist. All child psychologists can admin the test, BUT the results are subjective.
My son was tested twice for school entry. Once by a 'sub' (our psychologist was in a car accident and moved all her appointments to a colleague who DIDN'T specialize in gifted kids) and then once by the director of a gifted program who'd recommended the school (that needed the test results in the first place). He'd already done an 'unoffical' screen of my son ahead of time and was baffled by the paper results.
"OH." he said... and then proceeded to highlight everything the other tester had MISSED
"What goes faster a bike or a car?"
"Well MY bike goes over 160 mile per hour!"
"So which goes faster?"
"MY bike goes faster."
The tester marked the VERY BASIC question "wrong". But the specialist said; "This is super common with gifted kids. He's differentiating between HIS bike, and every other bike... AND I'm willing to bet your car tops out at 140-155."
"155"
"Yep. So he's ACTUALLY saying, 'cars are faster' but has done it in a totally typical way for gifted kids to; by making YOU think about it / providing and explination that "lays out" the answer for you."
He then went on to ask where the reading and math portions of the test were, and I told him she hadn't done those, and he was ticked. My son had been reading since he was 3, and doing math (just arithmetic, nothing fancy) since he was 4. But she didn't have him do ANY reading or math, because AGE WISE those weren't on the test. 2 years older those are on the test.
So two RADICALLY DIFFERENT scores, by two different professionals. Which is PART of why the gifted community loathes testing.
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Added: NOT all kids love kindergarten. My son was trying to take his own life in Kindergarten he was soooooo miserably bored, and spent hours every day crying. He had a FANTASTIC teacher. He was uber popular. He loved his friends... but he was quite literally bored out of his mind.