M.J.
January is the month to do it, but earlier, like right after new year's is best. I've gotten cheap stuff from Kohl's and Target this year. I got khaki pants from Target, size 4 for $3.24 and a sweatshirt hoodie for the same amount. I got a Winter coat from kohl's, Columbia for $30 and they are usually about $150.
I don't go to any outlet stores, just hit the regular ones and I have a price limit that I'll pay.
If you know you can just go up one size, it's good to do this, but I have gotten burned by someone growing more than I expected.