Some might call this a modulation (but that would really depend on other factors not conveyed by chord symbols alone) and this is why I said it depends on how you interpret 'release tension of the leading tone.' Certainly the tension of the leading tone relative to I is released when tonicizing IV, but you could also say the tension is being re-positioned to degree ^3 which then is the leading tone to IV.

In major that ascending tendency can also be weakened to allow a descending line, but instead of descending to the dominant, it would be common to descend to the subdominant like I V7/IV IV, or to put the changing ^7 degree in the bass, I V42 IV6. In minor that tendency to ascend can be weakened by lowering the leading tone facilitating a descending line, like a descending bass in i v6 iv6 V note that v6 is a minor chord. Let's accept the 'tension of the leading tone' to mean its tendency to ascend to the tonic. I read that Schoenberg said it was to release tension of the leading tone but if so why donвЂ™t we do this to all scales with leading toneД«ut it depends on how you interpret 'release tension of the leading tone' and whether you think various movements should be categorically grouped together. It doesn't apply to real music where the raised ^6 and ^7 degree are used in descending lines if the surrounding harmony is dominant.

You will be tested to give back that answer. Why do classical teachers often tell students to play melodic minor descending as natural minor?

All melodic minor scales