Usually, each class is “smaller”. For example, under a semester system, an engineering student may take 4 courses for a total of 16 semester credits of frosh/soph math. Under a quarter system, an engineering student may take 6 courses for a total of 24 quarter credits (= 16 semester credits, since each quarter credit = 2/3 semester credit) of frosh/soph math. However, some schools on the quarter system cram a semester’s worth of material into a quarter, but expect students to take fewer courses per quarter (e.g. instead of 4 courses, the expectation may be only 3 courses per quarter if each course is “larger”). Dartmouth appears to be an example of the latter.
Dartmouth is not that great a choice for engineering, since the ABET-accredited BE degrees usually take more than 12 quarters (4 academic years) to complete. (Of course, this may be less of an issue if the student wants to do the AB degree in engineering as a stepping stone to Wall Street or consulting.)