Drawing Resources

I was looking for some drawing resources for my studio students.  I found these helpful.

http://www.drawingandpaintinglessons.com/Drawing-Lessons/Pencil-Exercise.cfm

http://www.drawingtogether.com/Exercises2.html

http://carlosdamascenodesenhos.com.br/wp-content/uploads/2013/10/David-Lewis-Pencil_Drawing_Techniques.pdf

http://www.gsa.ac.uk/media/956631/guide-to-drawing.pdf