The spell creates a counter balance for the distrust in the target which may exist while being questioned by the caster. I.e. It causes the target to not distrust the caster. It absolutely does not cause the target to trust the caster either.
This spell is very useful to any caster as it causes the target to ignore any feeling of distrust. Those feelings could be present for a range of reasons which have nothing to do with the negative effects of the Gift. Therefore it is plausible to be useful to gentle gifted characters too.
The description is specific enough to guide when it's effects come into play and exactly what negative impression it is seeking to mitigate; meaning when the target is being asked questions. Not while being instructed or tutored and certainly not granting a positive modifier to social rolls.
If a mechanical effect needs to be calculated due to an ability check then consider how much distrust the target has toward the caster as opposed to all other reasons for a negative or positive reaction, and only mitigate the distrust.
Fear, gender bias, religious bias, visual presentation etc might also stack multiple factors to be considered which are outside the scope of this spell.
In looking at comments, I think there is a disconnect between the idea that a magic school is workable and exploring how to make it workable and assuming that such a school would fully replace apprenticeships as they are currently structured. Personally, I think all of my suggestions would apply only to some portion of new potential apprentices.
Some have posted arguments about why magi would prefer to train apprentices in the old system and put them to work on minor projects of their own when it is not working as lab assistants. I will accept that is true that some magi would prefer the old way of doing things, and that some apprentices would not fit into the new system and some traditions are incompatible with this, such as Bjornaer and Verditius. That doesn’t mean that some magi wouldn’t be interested in developing their apprentices along the lines I have laid out. Canonically, there have been attempts before.
With regards to crafting items and spells to overcome the impact of The Gift. The advantage of using magical humans as a target of these spells and effects is that they will not suffer warping as a result, whereas humans will be under a constant magical effect and pick up a warping point a year. So, if you can’t find a race of magic humans who are unaffected by the gift, you can create magic items which can overcome this penalty instead, but it seems to me you are still better off training immortal magic creature servants rather than dealing with humans who age and warp and so on.
A magical school, it seems to me, would differ from a mundane school only in that magic theory would be taught. So the question becomes whether it is worth losing a few seasons of service early on as well as paying for the schooling in order to get an apprentice who can be useful in the lab sooner. From the schools perspective the question is how many magi can it convince that this is true.
I wonder if a magical school might be better-designed as a university for journeymen magi, than for apprentices - a place where advanced Magic Theory, Latin and Artes Liberales can be taught and where a large number of primers and common Lab Texts are available for study - think Durenmar with more of a focus on teaching the basics to the newbies.
The only place where I can see a magic school for apprentices being of value would be one in Thebes for pre-apprentices who are waiting for Tribunal - those kids should start getting lessons in Attic Greek, Artes Liberales, Profession: Scribe and maybe Magic Theory. Similarly, I'm pretty sure Latin and that first step in Artes Liberales are taught in groups by master teachers wherever possible (a Magister in Artibus consors, despite the Gift penalty, is worth his weight in gold); a fosterage for Magic Theory group learning is not out of the question either (Bonisagus standard practice is for two apprentices to be jointly taught basic skills for the first two years in fosterage). But the apprentice system, both for the value of slave labor and because magi want filii, isn't going anywhere.
Probably, yes. Journeymen magi are in their 20's, have a Parma Magica and can expected to be responsible adults.
What the game needs, however, is a way for magi to study together; Arts cannot be taught except for one-on-one and there's no mechanics for group study of vis or hermetic tomes.
Hi,
Unless it was decided that the game needs to make sure that it is hard for magi to study together, whereby to better preserve the idea that magi tend to work alone.
Well, for junior magi, working together in the lab has some perks if they're led by a competent manager - though Hermetic culture and methodology makes this more difficult than it has to be, as the idea of separating "lead researcher" and "project manager" is a Solomonic innovation and Hermetic magi get absolutely no kudos for working as assistants - they don't even get the spell that's being worked on.
Still, take a team with a skilled lead researcher, add a scribe and follow up with a magic scriptorium, and a group who want a particular spell can get it fairly efficiently (this is particularly true if the magi involved have lower Art scores than they'd like, or if a group of specialists in their fields are collaborating).
While we're min-maxing here, why not get a very good scribe to take down your lecture notes?
A&A has rules for lecture notes, generating a tractatus with quality of Lecturer's communication + half scribe's Profession:Scribe. I once proposed this for "Gild Training" in the Rhine Tribunal - have someone with a high Comm teach on the relevant skill (like Code of Hermes, Area Lore in your tribunal) and not only are they pumping xp into the young gild members, a scribe is taking down notes to add to your Gild's pile of available tractatus.
Nothing min-maxing about it. It's a very good idea, especially if the Order, Tribunal or Covenant in your saga is together enough to have a school in the first place.
What about starting a mystery cult for the teachers?
There is a 'super good teacher' mystery cult in Lands of the Nile (Teacher of the House, pg 61), albeit for mundanes.
Just a thought.
There's probably a reason why House Jerbiton has not published a Mystery for the Gentle Gift, or why the Redcaps don't have a Mystery for Unaffected By The Gift, or for someone to have a Mystery for Good Teacher, but I don't know what it is.
Well, there is a canon Mystery Cult that can provide both Gentle Gift and Good Teacher. I think it's called Madres & Matrones.
You are incorrect about virtues being taught to more than one student at a time. pretty much ends the discussion of a magical school teaching Gentle Gift en masse, right there.
Except it does 't. It requires serious effort to teach, and could possibly preclude teaching other, useful virtues. I encountered this problem with my GG Mercere with Mutantum Magic. Even with Com 2 and Good Teacher, it required significant effort to get the teaching score up high enough to pass on both virtues without inflicting flaws. The cost of teaching the Gentle Gift means that you may not be able to teach other things that you would like to teach. While it seems "easy" particularly when someone throws down a teaching SQ of 30 or more, let's not forget the significant cost of getting a teaching score to that level. Com 5 requires a lot of characteristic points, a lot of virtues or a lot of via, or some combination of the three. Good Teacher requires a virtue, but this virtue is odd, that unless one is writing, it doesn't provide an actual benefit to the owner of the virtue. In addition, authors receive something of a delayed reward for the virtue.
Hi,
And, in a way, not even that, because stories are needed to unlock that reward... which is really no different from any other reward that comes from doing stories. That is, writing a text does not itself provide a reward, but provides excuses for stories that provide rewards.
So maybe Good Teacher is really a minor story flaw, providing a benefit and a source of stories.... 
/2
Anyway,
Ken
I think that's rules as intended. A magi CAN pass his hermetic virtues onto his apprentice, but will likely inflict his own flaws upon the apprentice in the process. I mean, so what if the apprentice picks up a few flaws? It builds character!
Oh, it definitely is! Part of what I was trying to do was to not pass on Magic Addiction...
But Magic Addiction isn't that bad, all in all. Unless your high level spells are really, really dangerous, and then you just haven't planned.