I don't mean to be a thorn but a spell checker is only really a band-aid for someone who has terrible spelling and its only a tool to help not completely fix your issues.
While The spell checkers are maintained by competent professionals (or so Id hope at least) they are far from perfect and they do not really "teach" how it is supposed to be done. Also the grammar checkers built into programs like word are terrible measures of grammar and arguably completely ignored except for periods and mechanical items.
I can understand learning difficulties and/or disabilities as well as dialects (like how I use Canadian English) but to really master it requires work, a good book on grammar and spelling and practice.
Desire helps too <.<
As for technical measures yes it can be done on a forum as there are spell check mods you can install. You could make it so that spell check is mandatory before posting but again machines are terrible for advanced language correction and some of the more competent writers will find zero tolerance on that frustrating.
Computer Flunks Hemmingway, Churchill, and Burgess