Introduction- What social class is and what the different types of classes. Examples of each type maybe?
You can also state which class has its advantages causing better achievement for the people of that class so advantages and disadvantages of both classes.
For example, working class has its disadvantages such as material deprivation and culture deprivation leading to under performance.
Middle class whereas has its advantages such as most being well educated so students having educated parents who can help, being from rich families so have resources need to study and perform well achieving more and better. There may also be a cultural advantage as most teachers or people with authority do tend to be from the middle class therefore favouring a certain type more. Do put both for and against points though such as there is also the fact that many people from the working class do also continue to higher education as a result of achieving better and getting good jobs!
You can conclude by reminding of the basic points and stating an opinion whether you think class affects achievement or not. Hope it helped