The school became aware of the incident when a video of the assault was posted online.
In a statement on the school's website, headmaster David Lovatt said a "concerned citizen" had sent the video to the school.
"The footage is extremely disturbing and in no way reflects the ethos or traditions of our school," his statement said.
"The assailants and videographers have been identified and will be dealt with." He refused to comment further.
In an e-mail to parents, Lovatt said KES had zero tolerance for intimidation, initiation, physical assault, fighting, bullying and other similar offences.
He warned that those found guilty would be suspended for a week and, on return, would face a further seven days' suspension from all school activities other than academic classes.
He urged parents to discuss the sanctions with their sons to help the school curb such incidents.
"I am no longer prepared to tolerate this kind of behaviour. We have tried through a number of appeals and educational processes to curb this, apparently to no avail. Now we will use a heavy hand."
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In the video, two boys stand nervously next to each other as two other pupils prepare for the assault. One of the older boys carefully takes off his blazer and rolls up his shirt sleeves. He then slaps one of the younger boys hard on the ear. The other bully does the same to the second victim. The two younger boys stumble backwards but do not fight back.
Several comments were posted on the school's Facebook page.
Pumeza Makasi Mamaregane wrote: "Bullies have no place at our school, or any other school for that matter. As a parent, the school has my full support."
Tihaam Chuckie Ahmed posted: "Heard they got suspended, a light judgment in my opinion."
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