Neoclassical theories of crime are something of a revision of the classical theory of crime.
The classical theory held that criminal acts are things that people choose to do of their own free will. Because of this, the way to control crime is to make that choice seem unpleasant. This was best done through making people fear the punishment that would follow committing a crime. The punishment should be consistent and proportional to the crime committed.
Neoclassical theorists essentially hold to these ideas. However, they understand that there are times when this classical model is flawed. The most important example of this is the idea that there are times when a person does not truly have the capacity to choose to act in a given way. Children and people who are mentally ill fall under this category.
Thus, neoclassical theories of crime are essentially like classical theories, with a few adjustments to recognize that people are not always able to choose.