What is the difference between a double and a single Bar/Bat Mitzvah?
B’nai mitzvah students do four major things on the day of their bar/bat mitzvah: chant Torah, chant Haftarah, lead parts of the service and teach Torah (deliver a d’var Torah). If it is a double bar/bat mitzvah, the main element that the students do together is leading parts of the service. The other elements (chanting from Torah, Haftarah and delivering a d’var Torah) are done individually. The order of students is determined by which part of the Torah portion they are chanting is first in the Torah.