TBL reverses PPP’s order: learners attempt a real communicative task first (with minimal pre-teaching), and the teacher addresses language needs after, based on what learners actually struggled with. It suits stronger classes and situations where you want to assess what learners can already do, rather than assuming they need a specific pre-planned language point. CELTA candidates are typically trained primarily in PPP but should understand TBL exists as an alternative, since assessors may ask you to justify your framework choice for a given lesson.