Doris Lessing's short story "Through the Tunnel" is certainly a coming-of-age story about a boy named Jerry. He feels very attached to his mother out of a sense of duty, especially since he is the only companion his mother has since his father's death and the only male in the family. Yet, at the same time, he is beginning to want his own adventures. In the story, his own adventure comes in the form of learning how to swim through the tunnel to the pool beyond the rocks like the local boys, most of who are older than him. Many passages help develop the theme of Jerry's growing maturity.
The first important passage reflecting the theme of his maturity can be found in the opening paragraph:
Contrition sent him running after her. And yet, as he ran, he looked back over his shoulder at the wild bay; and all morning, as he played on the safe beach, he was thinking of it.
In this passage, Lessing uses the term "contrition," meaning sincerely remorseful, to depict Jerry's devotion to his mother. He feels deeply sorry for wanting to abandon his mother because he senses she needs him, and this contrition keeps him at her side. Yet, at the same time, he is growing up and feels the urge to go off on his own.
The passage describing his decision to first "learn to control his breathing" can also be interpreted as depicting the development of his maturity. Jerry is wise enough to understand that swimming through the tunnel is a significant challenge and to know it will take training for him to be able to accomplishment the task. In addition, he's wise enough to see his most vital training step: learning to hold his breath longer underwater. A less mature, less rational boy might try to take on the tunnel immediately, without any training, killing himself in the process. Jerry is too wise, too mature to do such a thing.