...hiring someone that was once a great hitter doesn't always work out, and it surely won't work unless he's working with the right group of hitters on a certain team.
...getting stubborn batters to buy into what the coach is showing them is the problem...before every game during batting practice, players take some time out of the pregame session to hit a few balls to the opposite field and/or up the middle. So the ability to do so is obviously there. 
...unfortunately, the coach cannot make the hitter apply this batting practice drill to actual game time ABs. That mindset is ultimately up to the individual player himself. And stubbornly myopic pull hitting sluggers like Tex still insist on trying to hit through the shift, which plays right into the hands of the defense and hurts his team's chances of being productive.
		
		
	 
 
	
		
	
	
		
		
			Most great hitters are horrible coaches.... Just saying
		
		
	 
 
	
		
	
	
		
		
			...Ted Williams comes to mind.
		
		
	 
 
Ya'll are right pretty much spot on....
I've read in numerous sources, bios, even Wiki states, "Carew helped the Angels hit >.40 points higher during his tenure as Halo's Hitting Coach..." Yet no articles have provided the specific details to prove so....
I've looked at the Angels Batting Averages, (less the Pitchers inter-league at bats), and I just don't see it at all.
Sure the Angels did hit 40 points higher one year. Yet- those stats don't take into account the rookie Darren Erstads 1st year record, of obtaining more hits than any other Angel rookie in the history of the Org. It doesn't take into account ANY variables, like 2nd and 3rd year players, who finally found their swing, timing or groove. Doesn't take into account, roster changes, obtaining other players from outside the org, albeit FA's or Trades. 
Time equates to improvement in most matters, other than decadence, which often abounds in its own rite.
I've poured over those stats in the time frame Carew was the Hitting Instructor, and just DON'T SEE IT. Again, the statement quoted, lacks any and all specifics to prove its own point.
2ndly, had Carew really enabled Angels Hitters to improve their averages, then why didn't the same apply or happen, when Carew became the BrewHaHas hitting instructor????????? I don't see it, and:
Men manipulate numbers to their own advantage, to say what they want them to say, take shit make it look and smell like a rose, or take a rose and make it smell like shit.
Like life, the rose doesn't grow without that shit (fertilizer) and at times, we have to go thru the shit to smell the fragrance of life, otherwise their would be no rose buds....! 
I've seen several threads on how Ted Williams could not take his Senators and turn them into Hitting at will machines....IMHO, that says it all......!!!
"There is nothing new that we can say, poets (teachers) hands only re-arrange those flowers of word boquets"...