Sometimes people who enjoy life most, or else those who manage to find ways to enjoy life even when they know life is full of rotten things; are actually people who are very intelligent and who have learned how to find ways to find the positive aspects of life (while also being well aware of all the rotten stuff).
In fact, a lot of people (parents are often among them) who believe it is their responsibility to try to encourage a positive feeling in others by not being people who "suck the life out of" everyone they meet. Parents and grandparents often don't feel the least bit like being cheerful or doing something fun, but they'll actually make themselves enjoy life or at least appear to be, because they know how bad it is to be "toxic" to children and grandchildren.
The right parents will usually know how to raise kids who can cope with, put in perspective, and process the bad things in the world without becoming depressed (provided, of course, the child doesn't have "some mysterious chemical imbalance" that isn't anyone's fault. So, no. Education doesn't instill depression.
People sometimes mistake education for intelligence, and they aren't the same thing. Some even believe that no intelligent person can ever be happy. These are misguided beliefs. When someone gets "depressed" because of thoughts in his head it's often because he's not mature enough, or skilled enough, to be able to deal with those thoughts without becoming "overall" depressed. Teens and people have a tendency toward depression because their pre-frontal cortexes aren't quite finished maturing. Besides, they haven't had enough time to learn some kinds of living/thinking/coping skills.
There's "realistic" and there's "pessimistic". "Realistic leaves room for, acknowledges, and processes the good stuff as well as the bad. "Pessimistic" is a sign that something is wrong.
(Sometimes, though, schools can "indoctrinate" students into believing that "all is doom and gloom", and kids will often listen to them because of their role and/or their ability come across as if they know what they're talking about when they push all the "doom and gloom" in a way that isn't healthy for young people (who are, after all, impressionable when it comes to people they respect enough to listen to).