I might be making this more simple because I don't know how your data works.
I'm assuming that every student_ID only has 1 Structure_ID
So this is a simple relationship.
Make a query and add both tables. Click and drag from one Structure_ID to the one on the other table. This makes a relationhip(looks like a line). Double click on any fields that you want to show up (ex: Student_name)
In the "Field" row, in the a new colums enter
Code:
Balance: [tblFee_Structure].[School_Fees]-[tblstudent_fees].[fee_paid]
I think this is what you want, try it out and let me know if it works.