According to the certificated flight instructor, he and the student pilot of the Cessna 172S were practicing crosswind takeoffs and landings with an 8 knot, 90-degree crosswind. During the second landing attempt, as the airplane crossed the runway threshold, the student reduced power "more abruptly" than he had on the previous landing. The airplane "bounced," and the flight instructor told the student to add power. The student then "took out the wind correction on the ailerons and tensed up." The flight instructor then attempted to re-apply the left aileron control, and told the student "don't fight me." The student then added power while the flight instructor retracted the flaps from the 10-degree setting. The flight instructor expected the student to increase the engine power to full for a go-around, but he did not and the airplane bounced a second time. The airplane was at the far right edge of the runway, when the flight instructor assumed the flight controls and reduced the engine power to idle. The airplane continued off the right side of the runway, and onto a grass area, where it struck an embankment, and nosed over, resulting in substantial damage to the fuselage, wing spar, and firewall.