How is advancement to the next tier calculated?

[Emuchu]

League advancement is not caused by simple streaks as a lot of people used to believe. Every player has two ratings: your Points, that you can see, are used for League standings, but do not correlate to your actual skill rating. Your Skill rating is a hidden value that determines who you match with and, ultimately, your League. Once this hidden value reaches a high enough number, you'll start matching up against players from the next League, and if you continue doing well, you'll finally hit promotion.

Long story short, if you started at the bottom of your league (for example), it might be a while 'til you get out, but keep chugging along and you'll get there.