What is the ruling on studying in a mixed-gender school, and what are the implications of that?

If mixing (between genders) in the school is forbidden, and it involves open display of adornment (tabarruj) and leniency in looking (at the opposite sex), then studying in it is not permissible, unless there is a necessity and the student cannot find another (school), along with being safe from temptation (fitna). If there is no excuse, then the accountable student sins by continuing to study there. As for the non-accountable (student), he does not sin, but his guardian must search for another school to spare him from forbidden gazes.