For a long time, especially in my initial years teaching PYP PE, I stumbled my way through, trying to figure out how I should be teaching within the program. Mind you this was before the time that social media really took off, but the point is that I felt as though I had nobody to bounce ideas off nor colleagues to collaborate with.
Still to this day there is an assumption that PE is still very much a stand alone subject. I would strongly argue against this for a number of reasons, but one of the biggest would be the fact that 21st century learning is about developing the whole student. Effective teaching must address not only sport and fitness, but also the enduring concepts/skills that are transferrable across the curriculum. In the Primary Years Program (the PYP) there is a strong emphasis on transdisciplinary learning. This is achieved through the teaching of the transdisciplinary skills (see this link to learn more) which are broken down into 5 essential areas: Social Skills, Self-Management Skills, Gross Motor Skills, Communication Skills, and Research Skills.
The very nature of a transdisciplinary program requires extensive collaboration between the single subject and the classroom teachers, especially during times of integration with the unit of inquiry. The key to understanding that PE is not simply a stand alone subject revolves around the fact that other important links to the classroom curriculum can and should be made whenever possible. I have long been trying to integrate maths and language arts into PE whenever possible and this can be achieved through a wide range of tasks.
However, the responsibility to integrate maths and language arts is as much the classroom teacher's responsibility as it is the PE teacher's responsibility. Developing the whole child means that all teachers, both classroom and single subject, must collaborate both informally and formally whenever possible to ensure that authentic and genuine learning is taking place on a consistent basis. This means that the lines between subject area boundaries are blurred and blend together forming the foundation for a holistic curriculum in which students can truly acquire the skills necessary to move forward in the 21st century.