No Child Left BehindG 25

It's right in the achievement description but I've seen many people ask for clarification on this on many other boards and sites. Your buddy CAN be knocked out during the battle without voiding this achievement. The battle just cannot END while your buddy is still knocked out. Make sure to revive them before knocking out the last enemy, and you will be fine.

Some tips to keep in mind:
--Make sure to be careful when using attacks that inflict damage over time, like Burning, Grossed Out, and Bleeding. It's possible to void this achievement if your enemies have low health and one of these status effects, because if their attack finishes off your buddy, the status effect will hit them after their attack, and it could knock them out. If this finishes the battle, the achievement is voided.
--If you somehow do end up voiding the achievement, reload your last save and try again. This will put the achievement back in play. Saves get overwritten quickly though, so do this immediately.
--To be safe, don't end the battle with New Kid knocked out. The achievement specifies buddies, so it MAY be possible to end a battle with New Kid down as long as the buddy is still kicking, but I haven't tested this myself, and I couldn't find the answer anywhere I looked, so again, just to be safe, be sure both characters are on their feet.