Although preservice teachers are familiar with classroom life, they are largely unfamiliar with teachers' intentions and reasoning. Those completing a Postgraduate Certificate in Education (PGCE) have just one year to acquire new insights into teaching. This article investigates whether their school-based learning can be enhanced by preparing them to analyse the classroom practices of diverse teachers. A module used to augment work-integrated learning, "Teacher Choices in Action," has introduced more than 70,000 South African preservice teachers to key choices that all teachers make. They see how diverse teachers enact these choices through guided studies of recorded lessons. We use Legitimation Code Theory to compare lesson observation reports written by 83 PGCE preservice teachers at the start and end of completing this module. Initially, most participants gave superficial descriptions of classroom activities with basic explanations of what teachers do and why. Afterwards, their reports contained more complex interpretations of teaching, with more connections between their lesson observations and insights from their coursework. Guided lesson study potentially empowers them to interpret prevalent teaching practices and consider pedagogic choices for their lessons more thoughtfully and systematically, regardless of their educational backgrounds. It may also address some concerns about vastly different mentoring that preservice teachers receive during the practicum.