We teach the boys together for this using Brenda Ellis' 'Artistic Pursuits' series as our spine. http://www.artisticpursuits.com
The books are a series of projects, each focussing on a particular skill. There is a picture to study together at the beginning of each project too, which illustrates the technique used. This acts as a nice introduction to the history/appreciation of art and encourages us to look more closely at the painting than we may otherwise have done.
We also use Mona Brookes' 'Drawing with Children' as this gives more explicit instruction on the technique of drawing and Mary-Ann Kohl's 'Discovering Great Artists' for fun,looser projects using techniques inspired by great works of art.