Split Function And Multiple Select Drop Down

I have a multiple select drop down. It will load into it the following information: Student ID, Last Name, First Name

There will be another drop down box that loads with classes, only this is not a multiple select.

I need the user to be able to select all students they need from the first drop down and then select the class they want to insert them into. Then, when they hit the button, it will break up the data from the first, Student ID, Last Name, First Name and insert those three things into the database under those respective column names.

Does anybody know how I can split these up properly when there will be multiple students selected, or does anybody have a better way of doing this?