What the guy above fails to mention, and caused me to keep retrying this mission thinking the achievement was glitched, is that the DIFFICULTY must be on Classic, so I'll do the solution correctly. Once you're sure it is, boot up the mission "A Recruit's Duty" under Coral Lake East. My game seemed to be on Casual by default.
A side note is that once you're at the Missions main menu, with Missions, Multiplayer, Dragon Roost etc you cannot change options, you'll need to quit out the game completely (including quitting it from the dash, it can't be left in the background by simply hitting the Guide button), reboot it, and select Options from the first screen after pressing A at the main ident screen. I don't understand why this hasn't been patched, but there you go.
Click on Select Wingman, use Largo, you're good to go. Do as well as you can, you only need to get A ranking. If you manage to get S you'll also get the achievement. My first try I got B, and obtained the "Not Bad, Rookie" achievement