Unplanned Perimeter of Compound Shapes

After searching on pinterest for ideas of how to approach area and perimeter conceptually I came across this website:

http://www.theteacherstudio.com/2016/03/area-and-perimeter-studies-deep-thinking.html

Again moving away from my 'norm' of teacher talk at the start of a new topic the class were asked to use 12 tiles to make as many different rectangles as possible. The only input they had was the pre-assessment which showed none of them were secure with the concepts of area or perimeter. Through this hands-on task they were able to use the language needed for the week as well as skills of measuring. Nathalie was the first one able to see the connection between multiplication and area. It was a great introductory lesson.

The following day we moved to the 'cooperation' challenge found further in the teacherstudio website:
http://www.theteacherstudio.com/2014/03/perimeter-and-area-problems-cooperation.html?utm_source=feedburner&utm_medium=email&utm_campaign=Feed:+FourthGradeStudioLearningThinkingCreating+%28Fourth+Grade+S

A definite challenge, but I could really see a much deeper level of thinking. What I didn't think about though was the fact that this would lead them to thinking about perimeter of compound shapes. Not a year 4 objective. It was my 'a-ha' moment as I realised that through these type of investigations learning can happen accidentally, but naturally. And there I have been for most of my maths lessons standing at the front of the class 'teaching' concepts...