I bought 5 different jackets/sizes to compare. L and XL sizes for Classroom Big Boys (http://www.amazon.com/gp/product/B003AE8IDO), S and M sizes for Classroom Junior (http://www.amazon.com/gp/ product/B002D4ILFW) and Ultraclub Small Size (http://www.amazon.com/gp/product/B0031QS3Q8). The jackets for boys are true to size. I would say large is size 12-14 and XL is size 16-18. Junior Small is almost the same size as XL boys. The difference between them is that the Junior S cuffs are tighter than the XL boys. The junior also has a drawstring hood instead of a little stretch at the top of the hood.
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