Not sure how the single scheme/changed rules for very new entrants might affect this but for those paying Class A PRSI (everyone recruited after 1995?), the teachers pension and the state pension are separate but designed to work together to provide an accrual of 1/80th per year to a maximum of 40/80ths (50% of final salary).
From the asti website ( [broken link removed] ):
Pension:
In the case of a teacher paying A Rate PRSI, the pension is 1/200th of the pensionable remuneration that does not exceed the maximum personal rate of State Pension (Contributory) multiplied by 3.333333 plus 1/80th of the pensionable remuneration which exceeds that figure for each year of pensionable service. This is known as co-ordinated pension.
So (ignoring salary increases), with 40 years of service, a 60K salary and assuming the maximum state pension (SP) is 12K:
Salary = 60K
Max state pension 12K * 3.333 = 40K
Excess salary above 40K = 20K
Accrual per year of service = 1/200th of 40K plus 1/80th of 20K = 200 + 250 = 450
So for each year of service, 450 annual pension is accrued. After 20 years, 9K annual pension has been accrued (450 * 20 years) and after 40 years, 18K annual pension has been accrued (450 * 40 years). State pension is on top of this so if the person is entitled to the max state pension because of their PRSI contributions, they get 12K on top of their teachers pension. So after 40 years and a full state pension, total pension = 18K teachers pension plus 12K state pension = 30K which is 50% of final salary of 60K.
So to work out how much pension is accrued, you need to look at the two bits separately - the teachers pension should have a clear calculation (the relevant union website should show it) and then the state pension is dependent on the 'whole working life' prsi contribution record.
Also bear in mind that the concept of average PRSI contributions is disappearing fairly soon - being replaced with a total contributions approach (which seems fairer) - I think you get a max pension once you have 30 years of contribution regardless of average contributions per year.