Probably in the Parent/Gardian form after you have all of the required information. You could do it in the Close event before returning to the Student form. Frankly I do not have a great deal on experience with Many-to-Many relationships and I'm having trouble getting my arms around this one. (As if it didn't show)
1) the student information has to be added before the parent information
2) a parent can have more than one student ( we need only one parent for each student) so it's actually a one-to-many relationship
i did it the way I did only because when I tried to do it one-to-many (by adding the parent id as a foreign key in the student table) I have to add the parent id when entering student information
I was sort of hoping Pat or one of the other guru's would jump in with some useful suggestions. We can create all of the elements needed but I'm not sure how to present them. Maybe some googling will help and maybe another look at the NorthWind example.
Both of the samples are pretty straight forward. Each contains two forms each having a SubForm. Our example would be one form shows the Student and the SubForm shows all of the Parents/Gardians associated with this student. The other form shows the Parent/Gardian and the SubForm shows all of the Students associated with this Parent/Gardian. Your tab form is probably just fine as an interface. At least it sort of puts it all on the screen at the same time.
I think i'm going to change the structure back to One-To-Many (one parent can have more than a student in this school), I don't want the user to create the student, then the parent and afterwards" manually" attach their IDs.