Go out and fight the Armacham soldiers, about six of them. Collect ammo and move up to the building, and around the corner is a fight with four in the hallway; just go slo-mo and tear them apart with the ASP, they are weak to it. Nothing of note in the rooms, so go up and left.
The Armacham and Replicas are fighting, and it won't take long for the Replicas to kick ass. Go go to the door and from here mount your attack based on frags thrown to the armored Replica, hide, reload, and fire at him and company. He requires about two ASP clips, but the frags should speed it up and take out some of his pals. After the first one is down, two enemies will appear on the roof to the right, as well as a second armored Replica from around the fence to the left, so frag him once and unload slo-mo ASP rounds into him.
Feel free to swap your shotgun for the Hammerhead, and pick up the plentiful ammo around, as well as either of the armors around the area. When ready to move on, go around the fence to the basketball area and shoot the padlock on the barred cover to drop down and crawl into a room. In the library feel free to test the Hammerhead on the two waves of about three-four enemies.
Move down the hall as the doors are sealed. Not much but a med kit in the boys' room, and the path in through a hole in the wall in the girls' room. Pick up the intel, and go out the hall to more creepy ghosts and go right into the classroom for another intel. Go back and up the stairs. Some ammo to pick up and an injector in a stall in the bathroom. Go out through the utility closet.
Equip your proximity mines and kill one enemy to the left. The chopper will drop down about four enemies, so you can kill one with slo-mo as he rappels, then lay a mine in the area, and then another maybe. Then watch out for two soldiers on the roof to the left as you move along. Go around the path, up the steps, and hop over the rail onto a vent along the wall. Follow it and jump down through the broken window.
You will emerge at what I call the most hilarious part thus far - lines such as "take cover behind the donkey" and gems like "he's hiding behind the barn." Kill the two behind the barn, then the ones on the floor. Moving up there will be two to rappel down from the skylight, and two to appear from the cafeteria window at the end; I say just Hammer the guys as they come down the lines, then toss incendiaries at the other two. Into the kitchen there is an enemy to the right, and by either going left or right you will hit the main part of the kitchen with about four enemies. At the back you hear two more say they will bust through the door, so if you have one more mine left set it now, or use flames, or kill them straight up.
After all that, the Hammerhead should be low or out of ammo, in which case I say swap it back out for a shotgun and go collect a little ammo for it. Go through the door and pick up the intel, then go into the freezer and drop down. Yes, back to being scary. Just follow the path and shoot ghosts, and feel free to use slo-mo. Go down the hall, into the room, left, down the corridor, and in the second area go right and then to the left to shut down the gas using the valve. Upon returning your path is cut off, so shoot a lock to the right and go around to the burning desk, flip it over, and jump down; all the while fighting the ghosts of course.
Go up and through the door, then go right for armor and mines as vision returns to normal. Move down the hall and at the end you hear enemies, but through a door nearby is a quick med kit you may need. Use the sniper rifle down the hall to kill about four enemies before going right into the room. There will be three more enemies to kill, so be ready. In the upper right corner is an intel, then collect munitions and take the elevator.
Slo-mo and kill three Armacham goons, grab supplies and armor to the left, then pick up the intel in the room. Proceed until you see a dude go into the nurse's office. You have to go left to get a key. There are four to kill, so a frag to the right may help. Kill and go to the back to take the elevator.
This is a big, empty area with just ammo in the rooms. Just make it to the end and pick up the keycard. Yes, there goes the principal. Jump into his office and grab the two intels. Now come out and prepare to fight Principal Puppet. He's tougher than the rest, and for him I recommend the ASP. He will run all around the rooms and allow you chances to use the many gas cans to burn him. Feel free to lay mines, use flames, and just shoot him up in slo-mo. It takes a while, you need to follow him, and do kill his puppets or they shoot you.
Once he is dead collect any ammo, maybe pick up a Hammerhead if you see one, and return to the elevator. Call it and pry it open, then mash melee. Pick up any health before dropping down and returning to the nurse's office door. Go in and kill three enemies. Go up to the video area and pick up the armor and intel. Proceed and in the next room are four more enemies, three to the right and one in the room on the left. One more time to watch that nurse's video if you missed it the first time.
Pick up the armor and go into the nurse's office. Launch bluebird and end the level.