I think that’s actually too kind to training and certification since it implies that they’re useful when dealing with students at scale. The main benefit from learning about pedagogy was not in the application, it was in knowing the jargon for talking to other teachers and sounding like a professional. What’s annoying is that the jargon U.K. and US trained teachers use differs slightly.

You get better at teaching by teaching, same way you get better at painting by painting or playing music by playing music. You’ll get better faster if you’re paying closer attention to your students and what you’re doing and things like having someone watch your lessons and critique them or reviewing video of your lessons yourself afterwards helps enormously. If you want to be play violin an encyclopaedic grasp of music theory is less useful than another hundred hours playing until you get over 1,000 hours at minimum. Ed school lecturers and professors are not noted for their excellent teaching despite their presumably excellent grasp of theory.

My experience could be unusual, obviously, but what’s very unlikely to be wrong is the literature on the determinants of teacher quality which does not reliably find any effect distinguishable from zero for teacher training or for experience over six years.