Dad,
As this thread is already starting to reflect, there is no one way. By the time someone gets to college or Milb, I think everyone will agree, though, that they better be a really good hitter.
One factor I think is important to know is that as hitters move up to HS and then college, even though the quality of the pitching and pitches does get distinctly better, scouting reports, advance information, and learning better to adjust make big differences.
We start with the premise that you have to be able to hit.
Hitting comes from mechanics, repetition and confidence. Confidence comes in part from feeling you have command of that pitch and that AB.
In HS, I would agree your son needs to be a fundamentally good hitter with solid mechanics
While CollegeParent is correct that some college guys are 1st pitch hitters, that often times will come from advance scouting reports on the pitcher(pitching coach and philosophy?), and his tendencies and approach. If a lead-off guy is swinging at the first pitch of the game, more often than not he is confident because he has seen that pitcher before, has considerable scouting report information and is confident in both location and pitch selection.
For every situation like that in college, I think there are as many where the object is to see as many pitches as possible early in the game and be patient within the approach so other hitters learn from the AB and the hitter learns for his next AB.
Hitters can learn to be very good with 2 strikes if they learn and adjust within the AB and from AB to AB. Working an AB so the hitter has seen every pitch and especially the best pitch, by that point, gives an advantage to a hitter. Being in a 2 strike situation where you have not seen all the pitches and especially the best pitch leaves a hitter vulnerable.
Part of this is also within the context of the team, at the college level and above. Last weekend I watched a game where there may have been 35 or so scouts to watch a pitcher who is projected for the first round in June. He cruises 93-95 and touches 98-100. The approach against him was clearly to drive up his pitch count. By the 4th inning, he was close to 100 pitches, and out of the game. That ended up with a W for the hitting approach.
Part of this also involves command of the strike zone. While there is plenty about him to criticize, Barry Bonds might be the greatest of all time in showing patience, based on strike zone command, while also being aggressive. He would rarely go out of the strike zone and for more than a few years he might only see one strike in an AB. Between an unbelievable confidence(arrogance?), patience and aggressiveness, Bonds would take a walk if he did not get his pitch, but he would be incredibly aggressive on that one pitch in an AB where he controlled the pitch.
Not many are Bonds or close to him. Currently, one could compare Buster Posey, Marco Scutaro and Pablo Sandoval and see 3 completely different approaches which work.
As my reference to those 3 Giants will hopefully illustrate, when players get to college, I am not sure really good hitters necessarily have the same approach from AB to AB. Additionally, I am pretty sure a 2 hole hitter, for instance, might have a different approach than a 3- 4 and 5 hole hitter on a good hitting team. No matter what their approach, good hitters are constantly adjusting, but they are such good hitters they know they can hit in any situation.
Viewed from a different perspective, the better the pitching, the more they are in control if they know the hitter is one dimensional and does not adjust within an AB or from AB to AB.
If your son is in HS or entering, I would tend to focus more on mechanics, repetition and confidence. As he learns more about adjustments and controlling pitch counts and AB's, the issues between patient and aggressive can evolve. With that said, no matter what the count for a HS hitter, when he gets his pitch, he has to be aggressive unless the coaching call is for something different.