In what way would an educational course help though? I think the OP had in mind the case where people are abusing their kids in the worst possible form due to being incapable. For example, say there's a couple that live in an atmosphere of drink, drugs and clubbing and constant arguing along with low income. Let's also make the man short tempered. Are these people suitable for parenthood in their present state? Obviously not and it is these kinds of parents that would be prevented due to failing to meet set criteria, if there were to be this hypothetical license test.
Do you really think an education in parenting would help these guys? They have far bigger problems to work out and I don't think 45 minute a week self help lessons would do much good for them.
Not that I'm supporting the license, I'm just saying, education alone really isn't that strong a tool to prevent parents from doing something unjust/stupid.
Just take the recent case with the woman murdering her babies. Said classes would not have helped one bit (it's not like they would have taught her something basic like 'killing is wrong' :hmm: ). I suppose a license would not have been any better in this regard either.

Those cases are utterly disgusting and sick, but also quite rare. Practically, I'm not sure if such cases can be prevented in any ways, unless we change the world entirely as I doubt these people would even ask for help.
People in general need more knowledge about kids. If I hadn't taken the developmental psychology course in my school, I believe my thinking would be very different. Praise be to Allah I learned a lot about kids, their brain development, their understanding, their world and how different kinds of upbringings would affect a child.
Would the knowledge on these help parents? In my opinion it'd help those who are willing to understand children and raise them right. All people aren't like that.
Some parents still in this time abuse their children and punish them when they do wrong instead of communication. Nonetheless, parents that neglect their children aren't any better in the least. Don't you think these parents need classes?