At the very end of Jack's mission at Grissom Academy, you choose whether to send the students on the front lines, or use them as support roles. Sending them to the front line has them killed at the end, but they live if they're support roles.
If anyone knows the plot flag or id to do this, it'd be really helpful
The students in Grissom Academy serve as "War Assets". (I'm sure you've heard of "War Assets" in ME3). Anything or anyone you can ask to join your cause in repelling the Reaper invasion from Earth. The students will affect (not sure if greatly or minimal) the outcome of your Reaper repelling on Earth in the end of the game.