In higher education one learns to understand the world is not black and white, Especially in graduate school, people get accustomed to seeing things from different points of view, and reflecting on varied even opposing opinions. That naturally creates tolerance of differing opinions; instead of seeing conflict, one sees opportunities and expanded horizons.
I think people who are in higher education tend to be more tolerant. As you become more educated, you become more exposed to different viewpoints, and to how people might have come to those viewpoints. You learn to understand that many things are complicated and there may be more than one side to things. This makes you more tolerant.
Because individuals who obtain a higher education are exposed to more experiences, as well as different types of individuals, they do tend to be more tolerant in a variety of different ways. They tend to be more tolerant of differing opinions and beliefs as well as more tolerant of individuals with different backgrounds and experiences.
People with higher education may be less prejudiced than the population in general by a marginal rate, but higher education can lead to more intolerance of different views and ideas as one becomes more convinced that ones intellectual powers are stronger than the population at large. Also, many may shield their intolerance from criticism behind degrees that appear as evidence of forward-thinking. In short, any correlation when it comes to tolerance and education is not causation.
I believe universities and colleges do make an effort to teach tolerance or at least try and get students to understand positions from different perspectives. Unfortunately, some people pick these ideas up and assume the institute is somehow biased or wrong in their assessments. These people continue their life with an air of intolerance.
People with a higher education are not more tolerant if people with not such a high education. It depends on how the person was raised and the moral values that they have been instilled with. Knowing more information does not make a person be more tolerant to other people at all.