How to plan a model relation for collage admission app in rails

How to plan a model relation for collage admission app in rails
i want student basic Registraion&login
after login it redirects to student RegistraionForm conation student contact details and student marks forms

Student contactdetails form contains

student contact form
    first name
    last name
    address
    mobile no
    gender
    fathers name
    fathers occupation
    mothers name.  

Student marks list conatins

**registraion form**
    .
    |-- Board of examination
    |   `-- Branches(ex:science,:humanities)
    |       `--science[when i choose science]
               `--science subject1
               `--science subject2
               `--common paper for sciecnce and humanities
    |       `--humanities[when is choose humanities]
               `--humanities subject1
               `--humanities subject2
               `--common paper for sciecnce and humanities