Figures from the Dorset-based mutual showed it completed £9.1m of mortgages during the month.
This is 50% higher than August 2013 and represented the single biggest month of lending since Teachers was formed in 1966.
This rise in lending was funded by an increase in savings with more than £10m deposited during the month.
James Bawa, chief executive of Teachers Building Society, said: “We’re delighted with our August figures as the whole team has been working hard to deliver our plan for growth, alongside the truly personal service that we have a reputation for providing.
“The years immediately following the credit crunch weren’t easy, but we set a course for continued strength and took a prudent approach while the waters were stormy.
“Now that the outlook is brightening, we’re seeing some normality return to the mortgage and savings markets and I’m very proud of this result.”