If you go to Assign All of a Field under the student tools menu, you can assign Diplomas for a group of students.  

 

  1.  Menu> Student tools > Assign All Fields. Here you can select by Grade (so that you can select all Grade 12 students) or any other option that might work better for you: 
     

 

 
2) Another option is to create a new Excursion group first before you continue these steps. 
This way you know exactly who you are assigning the diploma to, in the step above. 

 

3) Once you select the group of students you wish to assign Diplomas to, Go to Selected fields > Achievement > Graduation requirement > diploma. 
 

4) Select your Diploma type (OSSD or OSSC) 

5) Select the Issuing school. 
 
6) Diploma data is usually June 30 (if this is the date that your school finished) 
 
7) click on Assign.