The rocket landed in a northern neighborhood of the city at around 7:30 a.m., shortly before the start of the school day. Another three rockets landed inside the city at around 9 a.m.
The Magen David Adom emergency services reported that several people suffered from shock.
Hamas' military wing, the Izz al-Din al-Qassam Brigades, claimed responsibility for the rocket fire. Sappers evacuated the remains of the rocket from the school's parking lot.
Some of the parents took their children back home, and the rest of the students went into class to start the school day.
Miriam Sasi, head of the education department at the Sderot Municipality, told Ynet that she had turned to the Education Ministry and asked to shorten the school day.
According to Sasi, there is a kindergarten near the school, and the teacher's assistant was there on her own.
"The kindergarten teachers only arrive at 8 a.m., and she stayed there alone and fainted. The parents and children had to attend to her. This is how we open the education system in Sderot every day, unfortunately.
"Today we were also informed that there is only one psychologist in Sderot on behalf of the Education Ministry, and I don’t know what to say. There is no mercy and no compassion for this city."
One of the parents told Ynet: "We arrived at the school, and shortly before entering we heard the Color Red alert system, and then a loud explosion was heard. Luckily, the children did not arrive at the school yet.
"What happened hear was real luck. If the rocket had landed 10 or 15 minutes later, a great disaster would have taken place here."
Running following Color Red alert (Photo: Amir Cohen)
Odelia Peretz, 31, a mother of two, said that "very loud explosions were heard, and it appears that they have simply improved the rockets. Once the hits were far away and we didn’t hear such explosions.
"There was a smell of fire in the air, just like yesterday when the factory was hit. Then we heard ambulances. They have simply improved the rockets."
Referring to life under a constant rocket threat, Peretz said, "We did not go to Eilat. I am a first grade teacher at the elementary school, and it catches me every morning. Yesterday there was an explosion during class.
"We barely study, we run to fortified room and then engage in relaxing exercise and let the children rest. My child is 3 years old and has not gone out to the yard for three weeks now. It's very difficult to manage a routine like this."
Half of children miss school
Education Minister Yuli Tamir visited the southern town Monday, and met with local school principals to discuss the difficulties faced by the town's education system.
The teachers told Tamir that due to the escalation in Qassam attacks on Sderot, only 50 percent of the students in town continue coming to school, while the other half fails to show up.
During the meeting, the teachers and principals said that many of the students are terrified and suffer from anxiety, and are having difficulties preparing for their exams. This mostly affects those students who are set to take their matriculation exams this year. The teachers reiterated to the minister their demand to fortify all the classes in town.
Earlier Wednesday, a Qassam rocket was launched from the northern Gaza Strip and landed near a chicken coup in a western Negev kibbutz.
Palestinian sources in the Gaza Strip reported Wednesday morning that Israel Defense Forces soldiers killed a Hamas activist near the northern Gaza Strip town of Beit Lahiya.
According to the report, the two are members of the group's military wing, the Izz al-Din al-Qassam Brigades. They may have been on their way to place an explosive device.
Ali Waked contributed to the report