Explain the motivation of Jerry’s mother in “Through the Tunnel” and how her motivation advances the plot of the short story.

Jerry's mother does not want to be the smothering type; she is worried that because she is the sole parent she has been "keeping him too close" to her. So, she tries to be loving, but provide him certain freedoms.

When Jerry and his mother walk toward the customary beach one day on their vacation, she notices that Jerry looks over his shoulder, and as he plays on the "safe beach," he thinks of the other one. So, the following day when it is time for their swim, she asks Jerry if he would like to go to another spot. At first, Jerry says "no" because he does not want to hurt her feelings, but then he blurts out that he would like to explore the rocks. So, she gives her permission for Jerry to go to the other beach alone. With this action Jerry's mother provides her son the opportunity to be more independent.

Another way in which Jerry's mother affords him chances for independence is by purchasing swim goggles, and not questioning him about his reason for wanting them. Further, when she talks to Jerry, she says things "casually" without dictatorial tones. On the day that Jerry completes his rite of passage through the tunnel, he returns home and rushes into the bathroom so that his mother will not see the bloodstains or tear stains on his face. After Jerry comes out, his mother just asks him, "Have a nice morning?" and she lays her hand on his shoulder momentarily. Then, she examines him more closely and is concerned, "How did you bang your head?" When Jerry answers "Oh, just banged it," his mother catches herself, thinking,

"Oh, don't fuss! Nothing can happen. He can swim like a fish."

By catching herself, Jerry's mother allows her son to retain his sense of maturity. As a result, he volunteers information on what he has been doing, "Mummy, I can stay under water for two minutes--three minutes, at least." She affirms his accomplishment, "Can you, darling?" But, she also cautions him lightly, "Well, I shouldn't overdo it. I don't think you ought to swim any more today." 

By allowing Jerry the opportunity to make his own decisions, Jerry's mother provides her son room to mature. This freedom advances the plot because she encourages Jerry to make every effort to go through the tunnel and complete his rite of passage. Perhaps, without the trust of his mother, Jerry might not have had the perseverance to have swum through the tunnel.