Rashford, 18, has scored seven goals in 13 games since bursting through with a double strike on his debut against Midtjylland in the Europa League in February.
He followed that with two goals against Arsenal and the winner in the Manchester derby against City in March.
There has been talk that he could force his way into England's squad for Euro 2016, but his manager said he had a lot of improvement to make.
"He can learn a lot," Van Gaal told reporters.
"You need always guts to put youngsters in the squad and also in the line-up but, of course, the academy and all the academy coaches have credit for these players, also the scouts who discovered these boys.
"I am a little part of it. But that part is very important because you need the guts to do that."
Rashford's big break was largely forced upon Van Gaal as United suffered a crippling mid-season injury crisis, which has eased in recent weeks.
The Dutch coach said that he has no new injury concerns ahead of Saturday's FA Cup semi-final against Everton, with only three long-term absentees set to miss the trip to Wembley.
“The squad is nearly fit. Only (Luke) Shaw and (Bastian) Schweinsteiger are unable to play and maybe (Adnan) Januzaj because he didn't play yet in the second team. But we have a full squad of fit players.”
So often this season, Van Gaal has had to juggle his squad as injuries mounted, but he has a different dilemma for Saturday's game.
"Every player wants to play in a semi-final," he said. "I have to select 18 players and I have now 24 players fit so I have to disappoint six players and that is not fine for a manager."
(Reporting by Toby Davis; editing by Ed Osmond)
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