There is a huge shift in tone when the mother reminisces on the past when her children would speak Spanish to hear, and they shared a common cultural connection. However we see that when the mother refers to her children's current state, and their disconnection from her the tone is more harsh and less figurative. The shift in tone is used to express the depression/sadness the mother is feeling now that her children do not speak Spanish anymore, and that she is now the outsider. We can tell that the mother is no longer proud of her children and that she wants to be a part of their "American" circle but she is too tied down to her roots to enable herself to do so.
Tone is expressed in this poem by the shift in the young boys realization of time when he actually touches the clock. At the beginning the author is very descriptive in what the boy is unaware of, and the symbolic meaning of the clock. Tobin is descriptive in the settings in which the boy will find himself once he understands the true meaning of time and age. The tone is also very calm and serene because it is proving the innocence of the boy and his ignorance to what time actually stands for. However when he finally touches the clock the tone switches and we see the boy taking action because he is able to say that "he is older now".