Grandson speaks Telugu at home but has never written it. Would Anglo Indian School suit him for class 3?

My daughter's family is looking at flats in Saroornagar for next year, and since I'm the one with free mornings, the school research has landed with me. Anglo Indian School is close to two of the flats they liked. Our grandson chatters away in Telugu with me all day, but his current CBSE school does Hindi as the second language, so he can't read or write a word of Telugu. If he joined a State Board school in class 3, how far behind would he be? Has anyone's child joined there from a CBSE school, and did the teachers give them time to catch up, or is it extra tuition from day one?