Teaching is a difficult task to get done right and involves a great deal of expertise to be done professionally. Some of this expertise can be gained prior to actually starting out your career, but this is mostly of poorer value than what you can learn in work for a number of reasons:

As with most standardised training, the goal is to standardise results, which, in the case of teacher training, results in teachers whom have a solid understanding of the basics. While the basics are essential, they aren’t always enough to produce great teachers. Likewise, not continuing formal training as a teacher, and relying purely on your own experience to develop your skills, will cause you to have gaps in your understanding of how to teach a classroom.

To develop your teaching skills, you should rely on a mix of formal training, for instance during teaching training days and various teaching conferences, as well as your own experiences. By using the formal training as a means to discover new ideas, you can then use your experience to determine which ones you’ll be able to apply easily and effectively.