My ds9 went there for part of pre-k when he was 5.

I liked the Clark School, though my son wasn't there long. Like all of these private schools, though, they cater to a certain market and particular types of kids/giftedness. If you've got the type of kid and giftedness that the Clark School caters to, then it might work out for you. Otherwise, it may not. And you may not fully be able to assess that situation until our son was placed in that school and setting, unfortunately. At least, I can confirm that the Clark School did pro-rate the tuition and fees within 90 days or something when things didn't work out as expected.

Feel free to pm if you like.