What Is Worth Knowing?

Critical Thinking 

As for my pupil...he judges, he foresees, he reasons in everything immediately related to him.
-Jean-Jacques Rousseau

The key that unlocks the treasure chest of education is being able to think for oneself. Above all else, students must learn to be independent, to teach themselves, because education doesn't (or shouldn't) stop after school is finished. French philosopher Jean-Jacques Rousseau recognized this in his treatise on the subject, Emile, or Education, in which he describes his ideal student, who is taught through concrete experience to investigate the world around him on his own.

Independence and free thought are all well and good; however, they are worthless without the ability to think critically, to analyze information and draw reasoned conclusions. So above all else, the skills of critical thinking and analysis are what is worth knowing in education. Critical thinking is also crucial to helping solve problems in one's society.

Society

I believe that the school is primarily a social institution. Education being a social process, the school is simply that form of community life in which all those agencies are concentrated that will be most effective in bringing the child to share in the inherited resources of the race, and to use his own powers for social ends.
-John Dewey

Progressive education reformer John Dewey believed that education was not a primarily individual or solitary endeavor but a social one: members of a society educate one another for the benefit of society.

The Educated Person is, in part,  someone who works to solve problems on behalf of their society. To do so, they must have critical thinking skills (see above) and must be motivated by virtues (see below), but they must also understand how their society functions. A person who does not understand, for example, how the American federal government works will not be able to advocate for the rights of fellow citizens, protect or build democratic institutions, or effect any other positive social change which requires the intervention or the permission of that government.

Virtues

I place virtue as the first and most necessary of those endowments that belong to a man or a gentleman; as absolutely requisite to make him valued and beloved by others, acceptable or tolerable to himself. 
-John Locke

The Educated Person is someone who can think critically and work to solve social problems, but they must also be motivated to do so; this motivation comes from virtue. English philosopher John Locke wrote in Some Thoughts Concerning Education that virtues are the most necessary element of an education, because having virtue is the only way to have a good relationship with one's society, or with one's own self. Certainly, without having things like self-discipline, kindness, or respect, one will have neither the ability nor any reason to do much to help others, or even oneself.

Instilling virtues, critical thought, and an understanding of society is the motivation for Good Teaching, and properly grasping and retaining these elements of education requires Good Learning.