Links for each type of scale will be in a menu below the guitar neck.
Why do guitarists need to practice scales? At face value, the answer should be obvious - to improve your finger dexterity, and develop some muscle memory. Being able to play a [insert pedantic scale of your choice here] front to back may very well impress your guitar teacher... because if nothing else it's an indication you've taken the time to work on them.
If you've been through my Basic Chord Theory for Guitarists document, you should already be familiar with the Key of C which contains no sharps or flats, and the intervalic formula (1, 1, 1/2, 1, 1, 1, 1/2) from which the Major scale is built.
What a _Music_ teacher will want is a bit deeper. Spending further time analyzing the patterns from which the scales are built will unlock a whole new world for you. No longer playing a rote memory bit over and over, you'll begin to improvise. The more time you spend with scales, the deeper your own personal connection to the structures will be... and you will also find your "ear" starting to sharpen up; that "sound in your head" ... you know the one I'm talking about??? The one you wish you could instinctively find the next note for, and the next? The more time you spend with these scales, the more it will open the entire guitar neck for you, and pretty soon - you'll stop _chasing_ those notes, and simply begin playing them as you think of them.
THAT is Magick!
I present the majority of scales in five positions, with the root note identified by a square. In time you will find you have favorites. Once you've identified a favorite, spend more time with it. Learn each of the five positions provided, then begin CONNECTING them to one another, because they truly live ALL OVER THE NECK.