According to Karan, Arjan plays Kajol and SRK's son in the film and he has been born and brought up in the US. In order to give the role an authentic feel, he had to be able to speak like the other kids there.
Which is why, when the film was being shot in San Francisco, a local teacher was hired there to teach Arjan.
There was no fixed routine to the classes; they were conducted whenever Arjan wasn't required to shoot. The classes were about three-four hours long and the teacher was paid USD 200 per hour. Arjan had 8 classes in total.