I'll give just a very short answer.
The salary scales for teachers are based on service and qualifications. So the difficulty that female teachers have is in catching up on the qualifications end. Being out of the workforce for periods of time does not enable them to undertake the same level of training as men are able to. Consequently, they are able to reach higher points on the salary grid than women do at much earlier phases of their lives. They may catch up, but overall, there's that pullback, and it affects overall pension and everything.