Mandatory Sentencing laws give a direction to courts as to how a person convicted of a crime is to be sentenced.
This is like a "one punishment fits all" for certain crimes, and removes the option for Judicial discretion in sentencing.
Mandatory Sentencing in Australia breaches at least two international treaties upon which Australia has signed:
- The Convention on the Rights of the Child - Requires that imprisonment of persons under 18 is of a last resort and for the shortest time possible.
- The International Covenant on Civil and Political Rights - Requires that no one is:
- arbitrarily detained
- subjected to cruel, inhuman or degrading treatment or punishment
- denied equality before the law
- deprived the right to have a sentence reviewed
There have been two instances of mandatory sentencing laws in Australia, however currently there is only one in force.
1996 amendments of the Criminal Code (WA)
Set a minimum sentence of 12 months imprisonment or detention for a third-time offense of home burglary.
1997 amendments of the NT Sentencing Act and Juvenile Justice Act (Repealed in 2001)
Imposed a mandatory sentence for property offenses based on past criminal records. Sentences all involved imprisonment ranging from 14 days up to 12 months in duration.
These laws are repealed after a change of government in 2001.
I hope that helps.
In regards to effectiveness, I haven't read any cases but I think you could mention it's effectiveness may be hindered using the argument that imprisonment usually results in a higher recidivism rate, and mandatory sentencing removes the judge's discretion in using other forms of punishment.