Well, i understand the 12bar blues, but im confused about what scale to improvise in...
Lets say we're in the key of C. so it will be C7, G7, and A7... but when during the A7 is played, do we still improv off the scale of D and when switched to C7 we play off of F, or does one just improv it all off the scale C...well if someone can answer that for me, it'll be great!
Hmm, I guess I'm not as familiar with the same type of 12 bar Blues as you, because I often find myself doing I-IV-V progressions... either way, if you are playing the chords you are playing, you could keep the solo in C Pentatonic Minor or switch it up with the chord changes and then the minor pentatonic scale to match the chord you are playing... but there are numerous ways to play these solos, i'd do what feels and sounds the best
Lyrics: Time wasted between solos.

After a mindboggling 3-hour Steve Vai concert, I had to listen to some brainless guitar playing... so I put on Nevermind...

Jesus Rocks!
my fault!! C7 (I), F7 (IV), AND G7 (V) i got mixed up, sorry but still one my teachers told me that due to F7 being a 7th chord that you should improv in the scale of Bb because F is the V of Bb, and the V is a seventh chord
I usually play the 12 bar blues with I-IV-V so in C it would be C, F and G, and I use the minor pentatonic (mainly) for that. So yeah I guess you could still use the minor pentatonic in C for the progression you're playing, but you could get all modal on it too, but I hate modes so I don't want to/can't explain that. Hope that helped somewhat.
Your teachers approach is a perfectly valid approach, a seventh chord is in a strictly diatonic sense always the V chord of a major scale.
So, C7 = C E G Bb, and C is the V of F, F major = F G A Bb C D E

You will also want to switch to the V of the next chord and so forth.