The exit polls oversampled educated voters in 2016, they admitted that and rebalanced things for 2018.
The real figures for 2020 likely will be closer to 2016 exit poll figures than 2018 figures. First, there's a pretty solid track record of college graduates making up more than 40-45% of the electorate in a presidential year that goes back well beyond 2016 (irrespective of past debates over whether "working class" people were undersampled). Also, there are age discrepancies at work that naturally reduce the percentage of midterm voters who are college grads.
Color me skeptical that midterm turnout differentials benefit non-college educated voters. I recall 538 finding that the opposite is in fact true.
It seems this trend held true in 2018, as at least per the Fox / University of Chicago Exits had 42% of the electorate being college-educated. Given past trends, it seems likely 2020's electorate will be slightly less college-educated than 2018's.
Admittedly there is a lot of conflicting data surrounding the education of voters at-large, but the chart above would suggest that there's a relatively small difference between the educational attainment of voters and non-voters, which contradicts a lot of other observations made via exit polls, polling and surveys in general.
Not necessarily: There are factors other than educational attainment at play, in particular age. Educational attainment is much higher among younger people (say, ages 26-35, done with college and maybe grad school but still young) than among older people (65+), but voter turnout among older people is much higher than younger people. Controlling for age, educational attainment is a huge factor in turnout. But, when not controlling for age, that's not the case, as a highly educated young person is less likely to vote than a low-education older person. Age explains why polls show the more educated a person is, the more likely they, holding their other characteristics constant, are to vote, yet more educated people and less educated people vote at about the same rate overall.
To some degree, race (and national origin), sex and income play into the equation as well, but age is the overwhelming other factor.
