There is a certain amount of uniformity that is necessary for a Q&A site like MO to work well. The aspects that make good/poor math questions are pretty uniform across major fields. There are already substantial differences between math and statistics, for example, enough to warrant a separate siteseparate site. I think math ed is similarly substantially different. (Note that there is already a proposal for an education site where math ed might fit better.) This may be disappointing but it appears to be the nature of Q&A sites like MO that guides these divisions.
replaced http://stats.stackexchange.com/ with https://stats.stackexchange.com/