If a student previously opted out of a Campaign and they are included in your new Campaign contact list, the student will be immediately opted out from the new Campaign and will not receive a text message. You will see the number of Contact opt-outs in Texting > Active > View then select the Analytics tab. The Engagement box will display the number of contacts that have opted out. 

Under the Contacts tab (also on the Texting > Active > View page) you can view the phone numbers the message was delivered to as well as the phone numbers that have opted out. 

To verify that a contact previously opted out, view the Contact Management > Opt-outs menu and cross reference an opt-out contact number from the new Campaign. You will be able to see a date stamp of when that phone number opted out.