The first question you have to ask yourself.. what does your teacher mean by "solid foundation". Foundation to what? To raise productive citizens? With the high divorce rate in countries like the United States, one could easily see that it is not. It is better for children to be raised within an "intact" family. The key word is "intact". A nuclear family is only a solid foundation if it stays "intact" and continues to provide a stable environment for the children.

A nuclear family consists of Mother, Father and kids. In many cultures, people live in extended family groups. Grandparents, aunts and uncles are live together. This approach has the benefit of helping support (emotionally, physically, financially) the married couple. The rate of marriage breakdowns are lower.

In other cultures, men have more than 1 wife. The extended family live together with each wife having her own "home".

There are also single parent homes, same-sex families… Was not Mr. Obama raised by a single parent? His grandparents?