Incredibly uncommon for 30 kids a class in elementary school. Also many students can barely handle arithmetic without massive handholding. Algebra in elementary school is out of the question
You are correct that 30 is on the high side, but I have seen classrooms in Philadelphia with 30 students to a single teacher ( 3rd grade, during the 2005 school year so it may have changed since then). However even at lower ratio's the point remains, you need to hand hold the kids, and we don't give our teachers the time or flexibility to do that.