Yes, basically there are two methods of promotion/demotion:
'old' way (they way I went through the game, none of this new fangled stuff) is to be either above 3.0 or below 2.0 (iirc) at the promotion date (and to be promoted you need to complete your 'minimum participation requirement')
The new, or fast-track, way is to get either above 4.0 or below 1.0 at any time (and having completed your MPR as above).
Note that you can't get demoted back to Rookie, it stops at D Class.
I recently got demoted from A to b on road due to being an idiot and racing too much when I just wasn't 'in the mood', always a sure way to rack up large incident counts by spinning at every third corner