I've just got DS7 signed up for Alcumus, but he hasn't started using it yet. On the Settings page
http://www.artofproblemsolving.com/liz/Alcumus/index.php?#settings
It says
"
Problem Difficulty
A lower difficulty setting will cause your topic progress and subject rating to move more slowly.
[ ]Easy
[ ]Normal
[ ]Hard
[ ]Insane
"
(It currently has Normal selected (by default).)
What exactly is it that this choice controls?
Any suggestions for what setting to choose?

For context, DS7 has just finished grade 5 maths (home/virtual schooling with k12.com). He hasn't "officially" done prealgebra yet, but he has self-taught himself much of prealgebra by playing around online. Most of what he has seen is "routine schoolwork", and he has not seen much in the way of "challenging problems".