The story is called "Let's Go Home." It's by Kewlian Sio, an Indian author of Sikkimese and Chinese parentage. The story was published in 1960 by Writer's Workshop, Calcutta, in Sio's collection Let's Go Home and Other Stories.
I wasn't able to find a copy of the story online, but I happen to have a print copy, so here's the first paragraph.
It started when they were going to school in the school-bus. Someone started to talk about marbles, and he was always so interested in marbles that, as he listened, he began to forget. At first only a little, but as the fervour of the discussion increased, he joined in the talk and it was then that he forgot completely. And afterwards, he did not know how he could have forgotten like that. But perhaps it was not so strange after all; everyone had always said he was "too sensitive" and "so absent-minded at this age". Perhaps it was he who was strange.
It is a very moving and well-told story, albeit somewhat slight. Since the point of view is that of a ten year old boy, the vocabulary and prose style is fairly simple. Probably for this reason, it's widely anthologized in English textbooks in India.
As proof whereof, here is somebody named Prakritee Kapoor with a discussion of the story and a question and answer session about it. Most of the discussion is in Hindi, which I think is an odd pedagogical choice if the idea is to teach English, but 🤷🏽♂️. Kapoor says the story is "Chapter 6 of class 8", so evidently it's still being used in a middle-school textbook, but I have no idea in which Indian school system.
Kewlian Sio was born in 1936 in Calcutta and attended school in Darjeeling. Sikkim was an independent kingdom until 1975. I have not been able to ascertain what citizenship Sio had for the first 39 years of his life. There is a large, long-established Chinese community in Calcutta and a large Sikkimese one in Darjeeling. Sikkim always had special status as an Indian protectorate, so whether his citizenship was Indian or Sikkimese probably didn't make much difference. And in any case the matter became moot after Sikkim joined the union.
Sio was one of the founders of Writer's Workshop, Calcutta. A blurb from the founding publisher, P. Lal, on the organization's website says:
The conceptual genesis of WRITERS WORKSHOP was in 1955. Immediately on passing M. A. in English Literature from Calcutta University in 1953, I joined St Xavier’s College, Calcutta, as Lecturer in the Department of English. Among my students in the 1st year B. A. were Kewlian Sio and Deb Kumar Das, both writing poems and stories. I decided to form a writers’ group. The plan materialised in 1958 when Pradip Sen, Jai Ratan, Amita [sic; should be "Anita"] Desai and William Hull joined, and a fromal “constitution” was drafted by Deb Kumar Das. A next-door Lake Gardens neighbour, P. K. Aditya, installed a hand-operated treadle printing machine, and the first books of WW writers began appearing, with I, Kewlian Sio, and D. K. Das as the three pioneer authors.
The book Sio published as one of the first three was A Small World, with Let's Go Home and Other Stories appearing two years later. Writer's Workshop became one of the most well-known and influential publishers of English-language literature by Indian authors, as well as of English translations from languages ranging from Latin to Manipuri.
Sio was publishing with Writer's Workshop as recently as 2010 (Bugged and Other Poems), but I have not been able to ascertain whether he is still alive.
Note: Meenakshi Mukherjee edited an anthology of short stories for use as, you guessed it, a textbook. That 1975 collection is also called Let's Go Home and Other Stories, but it's not the same as Sio's 1960 collection. Sio's "Let's Go Home" is just the first story and the remainder are by other hands.