Final answer:
The exact percentage of U.S. families fitting the student's specific criteria is not specified in census data. However, 66 percent of children under seventeen lived with two married parents in 2010, indicating a decrease in traditional nuclear families. The data also show a rise in single-parent households and diverse family structures.
Step-by-step explanation:
The specific demographic composition described in the student's question is not readily provided in census data; however, the percentage of the population that fits the general characteristics can be deduced from various statistics. According to the 2010 Census, 66 percent of children under seventeen years old lived in a household with two married parents, a decline from 77 percent in 1980. Although not all these families will fit the exact description (white European ancestry, middle class, Protestant, heterosexual, with school-age children, a stay-at-home mother, and a father as the primary breadwinner), it illustrates a decrease in the prevalence of the traditional nuclear family.
Moreover, the data reflect a change in family dynamics, with a rise in single-parent households and cohabitating parents. In the National Journal, it is reported that 13.1% of all U.S. families were headed by single mothers, indicating an increase in single-parent families. Additionally, there is a rise in extended households, unmarried and same-sex couples living together. Therefore, while the traditional family structure continues to be a norm, it is less predominant than in past decades.