IME, most parents will set some sort of bribe to encourage an underachieving kid. So the real question is, "Should schools step in and bribe students if the parent's can't?"

The answer is pretty clearly, "It depends on what you mean by 'bribe', and what you mean by 'do well in school'?" Paying kids to show up to class seems to work really well when it comes to test time. Paying kids to 'do well on tests' is completely ineffective.