Though both of these poems deal with family relationships, the mood and tone of each is very different.
First, the mood is the way the reader feels about the writing: it may come across as comic, serious or sarcastic.
The term mood is often used synonymously with atmosphere and ambiance.
Tone is defined as...
... the implied attitude towards the subject of the poem.
While the mood of a piece reflects the feeling the author tries to create in the reader, the tone is how the author feels toward his/her topic.
It should be noted that while mood and tone are often the same thing, sometimes they are totally different in a specific piece. While the author may seem to approach a certain topic with humor, he (or she) might well be making a point when one looks for deeper meaning, and discover that the author is actually using a great deal of sarcasm, which conveys a meaning opposite to the one perceived at first reading.
In Ben Jonson's "On My First Son," the poet is writing about the death of his first son. While losing any child would be devastating, Jonson lived in a society that greatly favored a son, especially a first-born son. According to the laws of primogeniture, all of one man's wealth (and even titles) would pass to the eldest son. England's Henry VIII is infamous for divorcing or executing wives in order to beget a son on to whom he could pass his name, throne and worldly goods.
Jonson seems to care nothing for primogeniture—he loses his son and writes this poem simply as a devastated parent:
...the poem poignantly stages the tension between the “poet’s” wish for this intellectual consolation and his emotional expressions of paternal grief.
Jonson notes that his son is his "joy." Research shows the boy was only seven when he died of the plague, while Jonson was away—something for which the author felt deep guilt. He had great hopes for his son: perhaps not just in the man he would one day become, but perhaps also in the belief that they had all the time in the world together spreading out before them. The mood and tone are the same: Jonson suffers the deep loss of his boy, noting that his son was "his best piece of poetry"—the best thing he had created.
On the other hand, "Marks" is a poem in which we may get a sense of one mood, only to change our minds by the end, providing the reader with insight to the author's tone. Pastan first notes that her husband has given her an A for the meal she cooked the previous night. By the next line we may sense a disturbing trend: he is critical about the ironing (unfinished) and presumes to evaluate her performance in bed! These first three items infer that the woman who is speaking is being judged, and not for who she is or her value as a person, but by how she "performs" her jobs or duties. The husband's behavior is seen in that of the children—who also judge their mother. The son gives his mom a C—noting that she could do better:
My son says I am average,
an average mother, but if
I put my mind to it
I could improve.
Neither does the daughter heap accolades on her mother—she simply notes that she is sufficient: she "passes."
The humor disappears when the mother delivers the closing line, which lets us know that she finds nothing humorous in the situation:
Wait 'til they learn
I'm dropping out.
While Jonson is a devoted father, agonizing over the loss of his son, Pastan's speaker is (we can assume) disgusted with her family, and seemingly prepared to leave.