As one student said: "At first he looked pretty serious, but then he started to do the rapping."
In class, Kajitani spins a bit of a rhyme into his teaching. He raps in class. For example: "Sit back relax let out a little smile because the rapping mathematician is the hot new style."
"I think he's weirder than me," one student said.
The rap continues. "No need for instruments or radio stations because I can break it down like order of operations."
"He's like one of the best teachers I have ever had," another student says.
Six years ago, Kajitani realized students had a hard time remembering math rules. But reciting Jay-Z was easy.
"I went home that night and wrote a song called "The Itty Bitty Dot" about adding and subtracting decimals," Kajitani said.
The rap goes like this: "Just line up the dot and give it all you got."
And he saw results. "Lo and behold at the end of the week my test scores shot through the roof and I've been math rapping ever since."
Another of his famous lines is: "negative to the left positive to the right it's the number line dance I can dance all night."
Students still react well to the rhythm. One said: "I used to get confused a lot in math but when he started rapping it all made sense."
His 26 raps - on everything from exponents to improper fractions - fill two CDs, now played in classrooms across the country. And of course, a rapper needs a music video.
Kajitani, just named a California Teacher of the Year, knows his formula for success.
"The number one way to get students to learn algebra and want to learn algebra is to connect it to their real life," he said.
He's making math hip, by giving it a bad rap.