OpenStax
Open Stax: Catherine Schmidt Jones: Half Steps and Whole Steps
Take a look at the two intervals of the half step and whole step and how they make up the chromatic and whole tone scales. This page includes a couple of self checking problems to test your knowledge.
OpenStax
Open Stax: Catherine Schmidt Jones: Scales That Aren't Major or Minor
As the title suggests, this site defines and gives examples of various other types of scales including chromatic, whole tone, blues scales and more.
Rock and Roll Hall of Fame
Rock & Roll Hall of Fame: Sti Lesson 44: Compositional Techniques
Young music students rarely see or, better still, hear a connection between the different types of scales, modes, intervals and other compositional techniques such as meter, tonality, and form used in both traditional 'Art' music and...
Other
Music Theory First Aid for Struggling Students
This site provides music theory information on such topics as rhythm, intervals, scales, chords, etc. Also, there is a fine section which describes the basic concepts of form and structure.
Music Theory
Music theory.net
An online beginning music theory and ear training site. This site is for students to use at home to reinforce what they learn in class.