What is the difference between these to sentences?
John wouldn't have needed extra lessons last month if he were as good at maths as you are.

John wouldn't have needed extra lessons last month if he had been as good at maths as you are.

Question

What is the difference between these to sentences?
John wouldn't have needed extra lessons last month if he were as good at maths as you are.

John wouldn't have needed extra lessons last month if he had been as good at maths as you are.

Answer

The meaning is the same, but the usage of "were" makes it seem more recent.  John is likely still not as good as you.

The usage of "had been" makes it seem more in the distant past.  John may be as good as you now.