As a high school art teacher I use a website/resource called the Virtual Instructor (
http://thevirtualinstructor.com) which offers free art lessons and tutorials. It offers tutorials/videos of drawing, painting and digital mediums for FREE. I have found these of great value to my students that may need a visual aid after I do my demonstrations for them before starting a project. It also has lesson plans for Middle/High School art programs, art courses (for a fee) for some of my students that want to go beyond the curriculum and many more resources.
A great resource for any middle/high school art teacher!