The chemistry experiment was dangerous yet the students forgot their safety goggles.
Add a comma between "dangerous" and "yet"
The main character in the novel is very complex she changes her mind constantly.
Add a semicolon between "complex" and "she"
The author describes the setting in great detail and then explained the conflict.
Change "explained" to "explains"
The high school principle announced the new attendance policy over the intercom.
Replace "principle" with "principal"
The marching band practiced for three hours in the heat, they were exhausted by the end of the day.
Replace comma with a semicolon
OR
Add "so" after the comma
Because the bus broke down; we were late for first period.
Replace the semicolon with a comma
Geometry is my hardest subject, I struggle with proofs.
Replace the comma with a period
I have drank three bottles of water during gym class today.
Change "drank" to "drunk"
I would rather write a creative story then write a research paper.
Replace "then" with "than"
A large group of excited students were waiting outside the gym for the pep rally to start.
Make no change
Please bring the following items to the exam a pencil, a calculator, and your ID card.
Add a colon after "exam"
The cafeteria stopped serving pizza on Fridays the students were very disappointed.
Add a comma after "Fridays" and add the coordinating conjunction "so" before "the"
When the bell rang, everyone rushes to their lockers to get their books.
Change "rushes" to "rushed"
The gloomy weather had a noticeable affect on the class's mood.
Replace "affect" with "effect"
The guidance counselor advised the student to except the scholarship offer immediately.
The large textbook with the torn cover, is sitting on the teacher's desk.
Remove comma between "cover" and "is"
The varsity team won the regional championship, they are going to state next week.
Add the coordinating conjunction "so" after the comma
OR
Replace the comma with a semicolon
The biology teacher teached us about cellular respiration yesterday.
Change "teached" to "taught"
The instructions were to complicated for us to finish without help.
Replace "to" with "too"
Because the weather was surprisingly cold we decided to cancel the picnic.
Add a comma between "cold" and "we"
I finished my essay early, I decided to proofread it one last time.
Replace comma with a semicolon
Don't forget to cite your sources plagiarism is a serious offense.
Add a period after "sources"
OR
Add a semicolon after "sources"
By the time the movie started, we had already bought our tickets and buy snacks.
Change "buy" to "bought"
You must remember that their is more to life than school.
Replace "their" with "there"
The scientist looked through the microscope she saw the bacteria moving rapidly.
Add a comma after "microscope" and the coordinating conjunction "and" after the comma