Evemomma I say pursue the achievement testing

...but then let your DS show you the way he wants to go with it.
My experience was slightly different in that I purposefully chose a play based preschool for DD so she could learn social skills. I sort of regret it because of the way it brought out her inner chameleon. I say "sort of" because none of us have any way of knowing where alternative paths would have led.
She used to corner me into enriching her at home (chased me with books, etc - I've posted about this before - how I used to hide from her to get a break). It was to the point where I enrolled her in skating just to try and balance her out and ease her focus on academics (not even kidding). She was PASSIONATE about learning anything school related, from very early on.
Although she had horrible, awful separation anxiety (screaming fits) whenever I would drop her off, she didn't mind going to the preschool. It was only twice per week, 2 hours long. The minute she realized she was the only one who could read or write she became a professional chameleon and even tried to convince me that she'd "forgotten" how to read.
Anyway, I sort of regret the path we took. Looking back I would have somehow scraped together money to have her tested and then looked for some kind of gifted program. Mind you, the way things were I never had any battles with the teachers over how to enrich her because she got what she wanted at home. Now in grade 5, however, she's not at all achievement oriented at school - she isn't motivated by grades. It's as if when I put her in the "social" preschool I placed her at the beginning of someone else's educational track and now she's sort of lost. The Chameleon has taken hold. I need to address this before she gets to high school.
Child-led is the way to go. Looking back, I feel like I should have listened to what my DD was clearly trying to tell me.