It's hard to remember how Algebra 2 started, because we had Geometry in the middle. I've asked my daughter about DO and Algebra 2 and she says it started ok, not too fast, but it quickly picked up pace, probably within a month. She felt prepared. I think the answer about the rigor is yes: DO is much more rigorous. We feel it gives much more exposure to types of problems. I will share my husband is a math guy and he is very impressed with the type of problems she sees in DO. hope that helps.