Take for example an IBDP horizontal team. One of the most important planning tasks for this team at the beginning of the school year is to create an IA calendar. If your students are supposed to be preparing for your IA, but they are also preparing for an IA in two of their other classes -- they most likely are feeling anxious, overwhelmed, and are unable to concentrate on doing their best. In order for student success, teachers need to create professional communities where they can discuss what they are teaching (and when they are assessing) their students.
Besides creating your IA calendar, a horizontal professional learning community can help you remove barriers to success for your students. If a student is struggling in your classroom, perhaps one of your horizontal team teachers can help you find a classroom practice that will help your student. In this way, your student can find success while you improve your own teaching practices and, perhaps, learn a new way to teach your curriculum.