It seems that screening for scoliosis in the U.S. varies from state to state, with some states having more stringent guidelines than others. Here in NJ the school screening starts in 5th grade at age 10 (elementary school) and I believe continues every other year, but I'm not sure up to what age. (It used to be an annual screenning, but budget constraints made it every other year.) My daughter's scoliosis wasn't detected at school because she was 10 in 4th grade. But, thankfully when I took her for her annual checkup at age 11 her pediatrician detected it...it was 17 degrees at that point. Within a few days she had had an x-ray and within 2 months she started seeing a pediatric orthopedic who specializes in scoliosis. A year later (every 4 - 6 months she had another x-ray/check-up) the curves had jumped to 24/23 and she began wearing a TLSO brace...that was over 2 years ago.
The initial screening required her to stand with her feet together and bend at the waist, letting her arms hang down. In her case, you could see one side of her back was a bit higher. The doctor had some kind of instrument that she placed on her back to measure, but it is different from the way the ortho measures the curve.
Just a note about the brace: it has proved to be effective in holding the curves but this past summer there was an increase as she had a growth spurt and basically outgrew her brace! She had a new one made. Right now she's getting ALOT of time in her back brace as she broke her right leg a month ago and has had a full length cast (and now leg brace). Hope this helps!