I'm not sure I remember all of it, but here it goes!
There's three categories: quizzing, activities, and challenges.
The quizzing is based roughly on your average study level. It takes just over 100% of your average daily level to get 100 xp points (1 level).
After that, doing the same amount of work gets you half the amount. After that, 25%, then 12.5%, etc.
Example:
You do, on average, 50 questions a day (well, correct questions).
Day 1: You do 50 questions, you get (about) 100 points
Day 2: You do 100 questions, you get 150 points
First 50 questions = 100 points
Second 50 questions = 50 points (half the previous amount)
So roughly, you can get up to 2 levels a day from quizzing along if you REALLY push it, but your daily average will climb as well, so it's hard to maintain 2 level a day.
The system for activities on the site works the same way, except you can get 30 points for a certain amount of participation), not 100 points.
The challenges are 10 xp a challenge, so max of 30 a day.
In total, if you push it all the way, you could theoretically get 200 (quizzing) + 60 (activities) + 30 (challenges)
In addition, there are modifiers you have (and some you can toggle) if you click your kao character.
Lastly, we DO have a new kao evolution in the works, it's just that this Japan>USA move really threw our work schedule through a loop.