Sandwiched between two tall lush juniors,...
Consider a comma after 'tall' because 'tall' and 'lush' are coordinate adjectives, meaning they are equal in status.
When I was thirteen, I let it bother me and I squandered a pretty good year railing at genetics and contemplating padded bras.
Consider a comma before 'and I squandered' because in this case, 'and' is acting as a coordinating conjunction between two stand alone sentences.
For one thing the main hallway at Wilbur High School is never teaming.
Consider a comma after 'thing' to show the introductory phrase of 'For one thing'.
but as soon as my eyes slide away my palms start to sweat as I wonder if I should have responded in kind.
Consider a comma after 'away' to show the introductory phrase of 'As soon as my eyes slide away'.
“Hey Rita.”
Consider a comma before 'Rita' because it is a direct address.
There are a half a dozen lockers between Rita’s and mine and she doesn’t hear my greeting.
Consider a comma before 'and she doesn't' to show that the conjunction 'and' is joining two independent clauses.
“Sure Maggie.
Consider a comma before 'Maggie' because it is a direct address.
Rita turns and carefully shuts to door to her locker,...
I think the first instance of the word 'to' should be 'the'.
Now that I know her date is Joe Thorpe. I’m even more surprised that she’s anxious.
Consider combining these two sentences. The first one is a great introductory phrase, so you could just use a comma instead of a period.
the grating high pitched giggles,...
Consider a comma after 'grating' because 'grating' and 'high-pitched' are equal adjectives. Oh, I also hyphenated 'high-pitched' because the two words make one complete thought.
Students entering the cafeteria singly quickly attach themselves to their respective groups.
I stumbled on the two adverbs back-to-back. Consider: Students entering the cafeteria alone quickly attach...
Just then the late bell rings and I mime call me then hurry to class. Poor Rita.
Consider placing 'call me' in quote marks to show that it is a specific thought.
Although they are a small group they take up several tables and the windows are their preserve alone.
Consider a comma after 'group' to show the introductory phrase.
His family isn’t well off but he’s a good athlete...
Consider a comma before 'but' because it is a coordinating conjunction between two independent clauses.
In a kinder universe the undernourished uber popular girls who have no fat to insulate them and tend to dress scantily would occupy these tables.
Consider a comma after 'universe' to show the introductory phrase.
Some of the girls are slightly overweight and they hide their ample figures beneath big flannel shirts that fall to their thighs.
Consider a comma before 'and' because it is acting as a coordinating conjunction between two independent clauses.
There were also a handful of predators that picked off a few weakened unlucky creatures.
Consider a comma after 'weakened' because 'weakened' and 'unlucky' are equal adjectives.
Instead of replying Rita rearranges the items on her lunch tray...
Consider a comma after 'replying' to show the introductory phrase.
Occasionally he tosses his head to flick the hair...
Consider a comma after 'Occasionally' because it is a disjunctive adverb.
Once he’s satisfied he twists around and tucks the triangle under the napkin dispenser.
Consider a comma after 'satisfied' to show the introductory phrase.
Instead I stare at my half eaten sandwich and pray...
Consider a comma after 'Instead' to show the introductory element.
She smiles but her smile wobbles a bit.
Consider a comma after 'smiles'.
In fact I am so angry I am very afraid I might start to cry.
Consider a comma after 'In fact' to show the introductory element. Also, the wording 'I am very afraid' seems too formal for her. Consider: 'I'm afraid'.
be the pity dater not the pity datie.
Consider hyphenating 'pity-dater' to show it is one thought. Also, I think 'datie' should be 'datee' and that it could be hyphenated as well: pity-datee. I'm not completely sure on the 'datee' part, though.
The lunch bell finally rings but it is too late to save me.
Consider a comma before 'and' because there are two independent clauses.
He is a no show for tests,...
Consider hyphenating 'no-show'.
“It's just dinner Mom.”
Consider a comma before 'Mom' because it is a direct address.
A few unimpressive snowflakes dust his dark hair making a mockery of my fervent wish for a blizzard.
Consider a comma after 'hair' to smooth the flow of the sentence.
I mean, I know this guy is comfortable in his own skin, but would it kill him to have a little consideration for the rest of us spazzes who aren't quite there yet.
Consider ending this with a question mark.
His story about the basketball team’s last trip to State is pretty interesting and after a long earnest campaign I wrangle a half-hearted promise from him to read the first chapter of The Good Earth.
Consider a comma before 'and after' as well as after 'campaign'. The first one is because of two independent clauses, and the second is to show the introductory phrase 'after a long, earnest campaign'. I also added one after 'long' to show that 'long' and 'earnest' are equal adjectives.
I’m a horrible judgmental person and tonight someone else besides me has figured that out.
Consider a comma before 'and' because there are two stand alone sentences.
We aren’t the ones risking everything for glory by scrambling up to the top of swaying pyramid.
I think you are missing an 'a' before 'swaying'.
The tea is uncomfortably hot and burns my tongue but I’d rather drink it than answer my mom’s question so I keep drinking until the cup is empty.
Consider a comma before 'but' and 'so'.