Left: Colours and boxes. Lyra Rembrandt Aquarell watercolour pencils. All doodles are in my Heinz Jordan 5"x8" Permanent Sketch Book.
I find that doodling while I'm in class actually helps me to concentrate on what the instructor is saying. I also seem to be incapable of having a pen and a piece of paper in front of me and not be writing or drawing. I just have to keep my hand busy.
Below left: Mandala with black and red overlapping scales. Sharpie Pen.
Below right: Detail of a page of overlapping circles. Staedtler Triplus Fineliners.