The students faced strict new security measures at the campus, implemented after the Feb. 14 attack by Nikolas Cruz that killed 14 students and three educators.
"We will have to go through security checkpoints and be given clear backpacks, my school is starting to feel like a prison," MSD student Sarah Chadwick tweeted.
In addition to the mandatory clear backpacks, provided by the Broward County School District, students also must wear IDs at all times and will be under an increased security presence on campus.
MSD principal Ty Thompson said in a memo to parents that entering the campus will be similar to entering "a sporting event, concert, or even Disney World."
Only four entry points will be available to students before school. After classes begin each morning, the front office will be the only available entry onto school grounds.