Drawing class

I've been taking a weekly class at the St Louis Artist's Guild (acronym SLAG, which makes me giggle) and the teacher, David Zamudio, has been gently working us towards drawing an actual human. Prior lessons focussed on spheres and cubes, working on shading and accuracy, this one was drawn freehand over about 20 minutes:

This week's lesson had us drawing a model of a skull, homework is five self-portraits. We do a lot of timed rough sketches, these ones took three minutes each:

I've been pleasantly surprised how not-impossible it is to draw a halfway decent thing given the right tools and some tricks on how to get the layout right. After that page of rough sketches, I really want to take the one at the top left and turn it into a proper robot head...