New2grammarThanks for the correction and answer, Clive
If a student is behind his/her/their class, he/she/he or she/they will normally do bad in the exams.
If a student is behind his/her class, he/she will normally do badly in the exams.
If a student is behind his or her class, he or she will normally do badly in the exams.
If a student is behind his or her class, s/he they will normally do badly in the exams.
If a student is behind his or her class, they will normally do badly in the exams. (the gender-neutral way)
Students who are behind their class will normally do badly in the exams. (Using the plural does away with the awkward constructions.)