In "Through the Tunnel," why does Jerry not tell his mother that he swam through the tunnel?
Jerry doesn't tell his mother of his accomplishment for two reasons. She is very protective of him. She treats him as a small child, even though he is eleven years old. She would be frightened and upset to learn that he swam through the tunnel. She might possibly watch him even more closely in the future. One theme in the story is Jerry's need to become more independent of his mother--to grow up.
Secondly, and perhaps more important, Jerry does not tell her because he does not need to tell her. Swimming through the tunnel is something he has done for himself to gain self-respect. He still wants or needs his mother's approval to some extent, however. At the end of the story, he does share with her how long he can now hold his breath.
By the conclusion of the story, Jerry has grown up in an important way. He has acted independently and proved to himself that he has discipline, strength and courage. Because this knowledge has now become a part of him, Jerry does not need to share it with his mother or prove it to the other boys.