QUOTE
(Thewall28304)
I could be wrong, but I get the feeling McGonagall doesn't hold the Weasley children in high regard. Not that she has anything against Arthur and Molly, it's just that the twins had already started giving trouble when the series starts. So I don't think she likes Ron very much either and feels he's not as good an influence on Harry as Hermione is.
Before the twins, though, came Bill, Charlie and Percy. Possibly the twins and Ron were a letdown to McGonagall after those three.
Now as to Ron being "not as good an influence on Harry as Hermione is," this may have been one of the few matters on which Snape ever agreed with McGonagall. For as I indicated in a recent PM exchange with your fellow Super Mod
Scout, the Trio dynamic was, believe it or not, very likely
Snape's creation! 
Consider. Snape, like practically every other faculty member, knows the blood status of each and every one of his students. And aside from being very clever, he's also an accomplished Legilimens. So into his first-year Potions class one September comes Harry Potter: not only a half-blood, but also (except for his eye color and, of course, the scar on his forehead)
the spitting image of his father, Snape's late enemy
James Potter! Into the same class comes also Hermione Granger: not only reportedly a brilliant student (as was the late Lily Evans, whom James "stole" from Snape,
and whose green eyes Harry inherited), but also a Mudblood (as Lily also was)! Already this week, Harry has had opportunity to see Hermione's scholastic prowess -- and to feel somewhat inferior to her on that account, though during the month before he boarded the Express he stayed up night and day with his new schoolbooks (a very Hermione-ish thing to do, as I've said before). What a setup...
To the living image of James before him, Snape proceeds to pose, none too politely, a rather hard Potions-related question. Immediately the Mudblood girl's hand goes up: how interesting. Is she just trying to show off her knowledge -- or is something else at work here? Potter's ignorance of the answer prompts Snape -- who at the same time pointedly ignores Miss Granger -- to deride him as having nothing going for him except fame. Snape then poses another hard question to Potter, again ignoring Miss Granger's almost desperate efforts to be noticed. Potter can't answer this one either, and pays for it by being unfairly accused of not having bothered with his schoolbooks before boarding the Express. Snape asks Potter another question: this time Miss Granger not only frantically waves her upraised hand, but rises from her seat! The worm turns here: though Potter can no more answer this question than he could the first two, he perceives that Miss Granger can, and respectfully suggests that Snape call on
her. For this, he's ironically accused of
disrespect, and accidentally costs Gryffindor a point...
Imagine now the following conference later that same freaky Friday, between Snape and Draco, in the former's office. First come the preliminaries (Snape knew Lucius as a Prefect, Lucius has spoken highly to Draco of Snape), then...
SNAPE:
Draco, have you become acquainted yet
with Harry Potter?
DRACO:
I'll say I have, Professor. What a stupid git
he turned out to be!
SNAPE:
Really? Tell me more.
DRACO:
I met him the first time at Madam Malkin's
the last of July. I didn't recognize him then --
I guess his hair covered the scar. He was in
Diagon Alley with Hagrid -- would you believe
he called that great oaf "brilliant"?
SNAPE:
Hagrid
is rather -- questionable, yes.
Go on.
DRACO:
Then I told him how Mudbloods shouldn't be
let in here. He didn't say anything to that,
but I could sort of feel he didn't agree with me.
SNAPE:
How interesting...
DRACO:
The next time I met him was on the Express --
I recognized him
that time. I was with
Crabbe and Goyle and I warned him about
making friends with the wrong sort of wizards.
But he'd already gone and got tight with
Ronald Weasley! SNAPE:
Unfortunate indeed...
DRACO:
The blood traitor wanted to fight us right
there. Potter just went along with him --
I'd have respected him more if
he'd challenged us. But nothing came of it because
Weasley set a rat on us -- it bit Goyle's finger.
We bolted then because we didn't know how
many
other rats they had in their
compartment.
SNAPE:
A wise move...
(Brief pause)
What did you make of Potter's -- chivalry
towards Hermione Granger in Potions class
this morning?
DRACO:
There's
another git for you, Professor.
Ever since the Express, she's been chucking her
weight about like she was a
Prefect! She
and Potter were
made for each other, if
you ask me.
SNAPE:
Indeed. So we're agreed that some sort of bond
seems to be in bud between them -- even if
they don't know it yet.
(Another brief pause)
You're aware that Miss Granger's Muggle-born?
DRACO (gasps, then):
I didn't think there could be anything worse about
her! It just figures, Potter standing up for a
Mudblood girl! Did you see her
grinning at
him with those buck teeth of hers right after?
SNAPE:
I did indeed -- though I don't think
he did.
And he's a half-blood, as you probably know.
(Brief pause again)
Any bond between Potter and Miss Granger, if
not checked in time, could lead to the destruction
of the Wizarding World as we know it.
(Slightly briefer pause)
I'm sure your father would agree, Draco.
(Draco nods vigorously. Another pause)
Now Ronald Weasley's a pure-blood. Have you
been able to find out how
he feels about
Miss Granger?
DRACO (snickers; then):
He likes her about as much as he does
me, Professor. He groaned when she was Sorted into
Gryffindor with him and Potter. Ever since then,
he's been bad-mouthing her.
SNAPE (brief pause; then):
It seems to me that he takes far more after his
brothers Frederick and George than after William,
Charles or Percy. And James Potter was in my year
when I was a student here: if his son's anything like
him, he won't be above breaking a school rule now
and again.
(Another brief pause)
Suppose the great Harry Potter were to be caught
breaking rules -- because his dear friend Ronald
Weasley dragged him into it. He
might be
expelled --
(Draco brightens visibly at this prospect)
-- and maybe Weasley along with him. But there'd
almost certainly be a wedge driven between him
and Miss Granger -- who, from what you've just told
me about her and what I observed about her in class
this morning, would have fought tooth and nail to
keep him out of trouble.
(Brief pause; then, smiling slightly)
I trust you can work out the details, Draco.
DRACO (still grinning broadly):
You can count on me, Professor.
Was Snape thus -- through Draco as his proxy -- the
real instigator of the "midnight duel" incident? I've said in the past that the "Potions Master" and "Midnight Duel" chapters of Book One followed each other a little too closely for comfort -- not to mention coincidence.
(
Note: The foregoing scene is a "clip" from my proposed fanfic, "A Hogwarts Horror," and specifically from Chapter Three, "The Untold Tale of the Prince." The story is patterned after Dickens's CHRISTMAS CAROL and takes place after Harry goes to sleep in Gryffindor Tower following "The Flaw in the Plan."
In Chapter One, "Dobby's Doubts," Dobby does the Jacob Marley bit, telling Harry in part that "Before a new Wizarding World can come, there remains much work to be done by many wizards -- including Harry Potter."
Harry sees the crapilogue and even worse (for one thing, Fudge is Minister for Magic again) in Chapter Two, "A Better World?" A Dementor, of all things, guides him through it all because apparently, both he and Hermione are destined to be de-souled over time -- and consequently, to drag down public morale in Wizarding Britain, which had recognized them as a potential power couple and force for reform!
In Chapter Three Harry's second spirit guide, none other than Igor Karkaroff, helps him find a heavily-sealed and threateningly-labeled bottle containing the above scene and other memories which Snape -- knowing that his association with Voldemort started out hazardous and only became more so with time, especially after Dumbledore's death -- stored away
long before Tommy-boy set Nagini on him, to insure that should he have predeceased Harry (not to mention Voldemort), Harry
wouldn't learn the truth about him. And yes, Harry gets to see Hermione smiling at him in that first Potions class -- and to reflect that even when she had buck teeth, she was always kind of cute...

)
Filch unfortunately failed to catch Potter, Weasley or Miss Granger out of bed, but Snape of course knew that they were the students Peeves had seen that night and subsequently raised an alarm about. Between this and the Remembrall incident (though the latter had the unfortunate side effect of gaining Potter the position of Gryffindor Seeker
and his own Nimbus 2000), a wall went up between the boys and Miss Granger, and seemed more or less solid.
But then came Halloween -- and the troll incident. It took weeks for Snape to piece together, from the grapevine, what had happened that day.
In that morning's Charms class, Flitwick had forced Weasley and Miss Granger to work together as a pair on Wingardium Leviosa. Their subsequent prolonged bickering, though half-whispered, could be so widely heard that even
Flitwick caught odd bits of it here and there: he said later that it seemed to be about something other than the proper performance of the spell. (Snape, remembering Draco's gleeful report of what had happened when the latter had issued his "midnight duel" challenge -- he could easily have stayed nearby to watch Hermione try to talk Harry out of it -- discerned that, in this Charms class, Weasley and Miss Granger had actually been fighting over Potter's soul.)
When the class ended, Miss Granger allowed Potter and Weasley to leave the room a minute or so ahead of her. In the corridor, she was confronted by a group of Gryffindor and Ravenclaw girls (the former reportedly including her dorm-mates Lavender Brown and Parvati Patil) who proceeded to bait her about "true love between you and Weasley...Only what would
Potter say?" and also about "drooling over Potter." Miss Granger then vehemently expressed her low opinion of both boys, justifying it by their apparent contempt for school rules, and adding, "If
I were Headmistress they'd have both been
gone by now!" The other girls then chastised her for being "full of herself," and for her twin obsessions with study and rules. One of the Ravenclaw girls (different accounts gave different names) then brandished her wand at Miss Granger, warning her that "you might end up with that big head of yours
looking its size.
Then see if Potter pays you any attention!" As the other girls burst out laughing, Miss Granger burst into tears and ran off down the corridor.
A few moments later, Miss Granger brushed past Potter and Weasley, almost knocking down the former. Potter, unaware of her clash with the other girls, attributed her distraught state to a derogatory remark Weasley had just made to him about her. Though Weasley responded defiantly to this idea, he nonetheless looked somewhat guilty.
Miss Granger was not seen in classes, or elsewhere, for the rest of the day. That evening, as students made their way to the Great Hall for the holiday feast, Parvati Patil was heard to tell Miss Brown that Miss Granger had been crying in a washroom since after Charms class and wished to be left alone. The two agreed that they for two were happy to oblige her.
Then came the news of the troll's presence in the castle -- and the frantic efforts of faculty and Prefects to lead the student body to safety. Potter was heard to point out to Weasley that Miss Granger knew nothing about the troll: he clearly intended to rescue her and, holding Weasley responsible for her predicament, to shame him into assisting therein. Weasley opposed the rescue mission, agreeing to it only on the condition that "Percy'd better not see us..."
Shortly afterward Snape, McGonagall and Quirrell arrived at a damaged girls' washroom to find Potter, Weasley and Miss Granger with the unconscious troll. McGonagall angrily demanded an explanation from the boys as to why they'd just nearly gotten themselves killed instead of going to safety in Gryffindor Tower. Miss Granger spoke up for them, claiming that she'd gone after the troll believing she could fight it off herself, and that they'd come looking for her; she then recounted how they'd collaborated to disable the creature. Snape realized that Miss Granger was lying for the boys, but there was nothing he could do about it. The three were all in McGonagall's House, so that lady contented herself with reprimanding the girl for her "foolishness" and taking five points from her; she then awarded Potter and Weasley five points each for saving Miss Granger.
Finally, Snape learned that Miss Granger had become friends with both boys; but while she had, to an extent, won Potter's
soul, Weasley had won his
study ethic. Potter had apparently learned his lesson from the "oblivious treatment" Snape had accorded Miss Granger in that first Potions class, but Snape told himself that it couldn't hurt to keep reinforcing that lesson, making it well nigh impossible for Potter to achieve -- in
his subject at least. In any case, Weasley had become a living wedge of sorts between Potter and Miss Granger; so if those two never became an effective study team, then their relationship would never be all it could be. Thus the Wizarding World's status quo would be safe for a long time to come; and as a fringe benefit, Snape would be spared the disservices of a
second insufferable know-it-all in that year's Potions classes...

Fast-forward now to Book Seven (putting this post at least nominally on topic). With Voldemort's puppet Pius Thicknesse in charge of the Ministry, Hogwarts (with Snape as Headmaster) is now compulsory for all wizard children of age to go there. But Potter and Miss Granger (Weasley reportedly being sick at home) seem to have disappeared from the face of the earth! How?
If Phineas Nigellus could tell Snape about Harry and Hermione being in the Dean Forest, why not also about Ron having accompanied them -- and having
abandoned them, thus opening the door for the
eventual formation of the "dangerous" Harmony dynamic?
If Snape could send out Lily's Patronus to guide Harry to the (real) Sword of Gryffindor, couldn't he also enchant the Sword to lead an unsuspecting Ron to the woodland pool where an equally unsuspecting Harry would
just happen to find the object? Then the Trio dynamic would be restored (albeit not smoothly), thus keeping the Harmony dynamic neutralized.
Wouldn't the red rodent have just
loved all this irony: himself as Snape's pawn and Snape as his enabler?