The Leaches' younger brother and many of his classmates from the class of 1971 advanced and continued the movement. Students from the class of 1972 and 1973 collected pumpkins typically no smaller than a basketball and dumped them out of the backs of their cars and watched them roll down the steep hill. The class of 1976 dumped around 900 pumpkins.
The passage describes a tradition of pumpkin rolling that started with the Leaches' younger brother and his classmates from the class of 1971, which was then continued by students in subsequent classes (1972, 1973) who collected large pumpkins and dumped them down a steep hill. The class of 1976 played a significant role in this tradition with over 900 pumpkins.