Robson takes charge after spending last season as No2 to former manager David Moyes.
Robson told the club's website: “I enjoyed my time with the first team last season, and I was grateful for the opportunity. It gave me a chance to work closely with some top international players and enjoy some new experiences, including the challenge of European club competition.
“However, I am really looking forward to being involved with the Under-21s again. Working with young players is something that I obviously have a lot of experience in, and a great passion for. I love coaching and the challenge of helping players to improve, and I am excited about the prospect of developing players who will be the future of West Ham United.
“The last couple of years has been a really successful period for the Academy, and there are some very talented young players coming through. Nothing gave me greater pleasure last season than seeing George Earthy and Kaelan Casey make their Premier League debuts and we want more of that.
“West Ham is my Club, and I know how much it means to our supporters to see homegrown players coming through the ranks to make an impact at senior level. It is a big part of our identity and heritage, and I am very proud to have that responsibility.”