Free Shark Beast by Russ Cooper

Lancy.
    Then, and only then, did Miss Babcock finally scream.
    It instantly lunged for Miss Babcock, but somehow, impossibly, it missed. Meanwhile, Miss Babcock, all 292 pounds of her, swivelled around on those pigeon toes of hers, and was mad-running down the cement walkway toward the still-open school front door. It was an impressively grotesque sight -- so much excess human flesh bobbling and wobbling -- she seemed almost like a pink-hued version of the goopy creature that was now slither-bobbing after her. Miss Babcock's mouth was open in the shape of a beyond-terrified scream, but no sound was coming out -- both the boys gaped through the smudge-glass, as if from the insides of their own personal overwhelmed Simpson's Treehouse of Terror--
    Then, a switch snapped in Derrik's brain.
    He pulled the door closed -- hard.
    "But Miss Babcock needs to get --" Ryan started, but was stopped silent as Miss Babcock hit against the door (as if she expected it to open inward), and the whole front of her body went flat against the glass with a sickening, fleshy SLAP.
    Ryan staggered back a half-step, mesmerized by the distorted, smudgy version of the school's front office secretary splatting against the door, her face and lips Silly-Puttying against the glass, as her drooling, muffled voice commanded, "LET ME IN YOU LITTLE RAT --"

    Whatever else she said flooded away in a whirlpool of a shriek.
    As gruesome as Gina's death was, it didn't compare to what happened next, close up, right against the glass, as suddenly the door looked like someone had dumped a barrel of Vaseline on it, all over and around Miss Babcock. Impossibly, she pressed herself even flatter against the smudge-glass, her teeth gritting, and muscles-out-of-nowhere tightening in her face and neck and... and then, she went slack. Just like that. Her body stayed pressed against the door, but no longer under her own power. The "Vaseline" around her thickened, and Ryan winced -- it looked like fifty kids had all sneezed against the window in gross unison -- and her body, still pressed against the glass, twitched slightly, to the left, to the right...
    ( It's chewing her, he realized with stomach-hollowing resignation)

    And, simply put...
    Miss Babcock began to peel.
    ~~~

    When Miss Babcock was finally gone, every last ounce and scowl and wrinkle, the goopy creature slithered back from the window, spit out a pair of black trifocals, and then, casually, bobbled away from the door, paused, spit something else out, and, with a satisfied shimmer, wobbled out of the door's view.
    Derrik looked at Ryan.
    Ryan looked at Derrik.
    And, with a scream, they both went running down the front hallway.
    ~~~

    "Dude! What are you doing!"

    "The principal's not here," Ryan grunted, climbing over the counter into the front office. "Nobody's here. All the offices are gone-empty! Everything's locked!"

    "What? Where are they!" Derrik's jaw popped. "Did they... did that thing ... get them?"

    "No --" Ryan slipped and fell into the office with a clumsy CRASH. A few seconds later, he was on his feet at Miss Babcock's desk, heading for her multi-line phone. "The pep rally... the stupid pep rally... stupid Homecoming... they're all in the stupid gym ..."

    "No way, dude! No freakin' way!" Derrik slammed his fist down on the counter. "YOU want to go, fine. I'll buy flowers for your funeral. But no funk-a-freakin' WAY I'm STEPPING out of this building."

    Ryan threw him a sour look. "Man, I'm not saying we should leave. I'm in no hurry to get out there with that thing either. I'm just telling you where everybody's at and why they ain't here, okay, dude? Now stop the freak-out and let me see if I can get a hold of somebody..."

    "As long as we do it inside, that's fine!" Derrik, feeling suddenly very uncomfortable alone in the hall, starting climbing over the office counter.
    "That's what I'm sayin', idiot," Ryan muttered, taking in the phone system. "Let's get some help going here..."

    "Hey, dude!"