From The Case of Education.  Written pre-Trump.

Abundant research confirms education raises support for civil
liberties and tolerance, and reduces racism and sexism.[1]  These effects are only partly
artifactual.  Correcting for intelligence
cuts education’s impact by about a third.[2]  Correcting for intelligence, income,
occupation, and family background slices education’s impact in half.[3]  All corrections made, education fosters a
package of socially liberal views.

At the same time, abundant research also confirms education raises support for capitalism, free
markets, and globalization.[4]  These effects, too, are partly
artifactual.  Correcting for intelligence
cuts education’s impact by about 40%. 
Correcting for intelligence, income, demographics, party, and ideology
halves it.[5]  But when all corrections are done, education
fosters a package of economically conservative views.[6]

If educators are as left-wing as they seem, why would education
have such contradictory effects on students’ stances?  The charitable story is that educators keep
their politics out of the classroom.  The
more plausible story, though, is that educators are unpersuasive.  The Jesuits say, “Give me the child until he
is seven and I’ll give you the man.”[7]  Society gives liberal educators the child
until he’s fifteen, eighteen, twenty two, or thirty.  But issue-by-issue, teachers are about as
likely to repel their students as attract them. 
Educators could protest, “The problem isn’t that we’re unpersuasive, but
that students are stubborn,” but students revise their opinions all the time.  The longer they stay in school, the more they
revise.  They just don’t revise in a
reliably liberal direction. 

Critics who highlight educators’ leftist leanings usually have an
ideological ax to grind (or swing): “Leaving education of the young in the
hands of ‘politically correct’ ideologues endangers our democracy.  School should be a vibrant marketplace of
ideas, not a center for indoctrination.” 
Though they’re right about the imbalance, it’s a paper tiger.  Even extreme left-wing dominance leaves
little lasting impression.  Contrary to
the indoctrination story, education doesn’t progressively dye students ever
brighter shades of red.[8] 

Since education raises social liberalism and economic conservativism, neither liberals nor conservatives
should cheer or jeer education’s
effect on our political culture.  What
about people who are both socially liberal and economically conservative?  Should they admit that education really is
“good for the soul” after all?  It’s
complicated.  If teachers aren’t molding
their students, the logical inference is that students are molding each
other.  But peer effects, to repeat, are
double-edged.  When schools cluster
socially liberal, economically conservative youths inside the Ivory Tower, they
inadvertently but automatically cluster socially conservative, economically liberal
youths outside the Ivory Tower.  If education is good for the souls of the
former, it’s bad for the souls of the latter. 
Net effect on the polity?  Ambiguous.

See e.g. Coenders et al.  2003, Weakliem
2002, Nie et al. 1996, Golebiowska 1995, and Case and Greeley 1990. 

Nie et al. 1996, and Bobo and Licari 1989.

[3] Kingston
et al 2003.

Caplan 2007, 2001; Weakliem 2002. 
Althaus 2003, pp.97-144 similarly finds better-informed people are more
economically conservative, all else equal.

Caplan and Miller 2010, pp.636-47, plus supplementary calculations from the authors.

Measuring effects issue-by-issue neatly explains education’s puzzlingly small
impact on ideology and party.  Since
education simultaneously increases social liberalism and economic conservatism, its effect on “liberalism” is
ambiguous.  And while their social
liberalism makes the well-educated more Democratic, their economic conservatism
makes them more Republican, leaving partisanship nearly untouched.

AzQuotes 2016.

Lott 1990 argues dictatorships spend more on education in order to indoctrinate
their citizens; Pritchett 2002 argues that this indoctrination motive explains
why all governments produce
schooling.  Plausible claims, but they
hardly show the indoctrination is very persuasive.