The teenage midfielder has signed a two-year professional development contract at the Weston Homes Stadium after graduating from an Academy he joined at the age of nine.
Van Lier is expected to join Matthew Etherington’s under 23 Posh squad next season. He made a handful of appearances for them last season.
Academy manager Kieran Scarff told the Posh media team: “Will has got lots of energy. He likes to support the attack, but will do the defensive side of the game. It is fantastic he has progressed through all of the age groups to where he is now.
“It is a long journey. His parents have been around the club for 10 years too. Will has just got to carry on his development, work on the areas where he needs to improve, listen to the coaches around him and build on his attributes.”
Van Lier added: “I am over the moon. It has been a real journey, but to get to this point is a dream come true. It is all I have ever wanted. When you first start out in Academy football, it is a little surreal, but you are just playing football and enjoying it. As you progress it becomes more serious and now I have the opportunity to develop further around a professional environment.
“All the work has paid off and I can’t wait to grasp the opportunity. The first year as a scholar was a bit disappointing for me, but I feel I have kicked on in the second and I have really enjoyed it. The challenge now is to kick on again and try and get as much game time as I can.”
Posh have now seen five players from last season’s under 18s earn professional development contracts. Goalkeeper Will Lakin, centre-back Harry Thomas, full-back Oscar Tonge and midfielder Hisham Chiha are the others.