The Sydney-born 19-year-old has made the switch to Loftus Road from Palm Beach Soccer Club in his native Australia.
According to the Championship club's official website, Wallen will initially link up with the development squad in West London.
The youngster, who was previously on the books of Premier League side Watford, has agreed a contract until June 2017.
Restore Data
| Team | P | W | D | L | F | A | GD | PTS | |
| 1 | Leeds UnitedLeeds | 29 | 17 | 9 | 3 | 53 | 19 | 34 | 60 |
| 2 | Sheffield UnitedSheff Utd | 29 | 18 | 6 | 5 | 40 | 21 | 19 | 58 |
| 3 | Burnley | 29 | 15 | 12 | 2 | 36 | 9 | 27 | 57 |
| 4 | Sunderland | 29 | 15 | 10 | 4 | 42 | 24 | 18 | 55 |
| 5 | West Bromwich AlbionWest Brom | 29 | 10 | 14 | 5 | 38 | 25 | 13 | 44 |
| 6 | Middlesbrough | 29 | 12 | 8 | 9 | 47 | 36 | 11 | 44 |
| 7 | Blackburn RoversBlackburn | 29 | 12 | 6 | 11 | 32 | 28 | 4 | 42 |
| 8 | Bristol City | 29 | 10 | 11 | 8 | 37 | 34 | 3 | 41 |
| 9 | Watford | 29 | 12 | 5 | 12 | 40 | 41 | -1 | 41 |
| 10 | Sheffield WednesdaySheff Weds | 29 | 11 | 8 | 10 | 42 | 45 | -3 | 41 |
| 11 | Norwich CityNorwich | 29 | 10 | 9 | 10 | 48 | 42 | 6 | 39 |
| 12 | Coventry CityCoventry | 29 | 10 | 8 | 11 | 39 | 38 | 1 | 38 |
| 13 | Queens Park RangersQPR | 29 | 9 | 11 | 9 | 32 | 37 | -5 | 38 |
| 14 | Millwall | 29 | 9 | 10 | 10 | 28 | 26 | 2 | 37 |
| 15 | Preston North EndPreston | 29 | 8 | 13 | 8 | 32 | 36 | -4 | 37 |
| 16 | Oxford UnitedOxford Utd | 29 | 9 | 9 | 11 | 33 | 43 | -10 | 36 |
| 17 | Swansea CitySwansea | 29 | 9 | 7 | 13 | 32 | 40 | -8 | 34 |
| 18 | Cardiff CityCardiff | 29 | 7 | 10 | 12 | 33 | 44 | -11 | 31 |
| 19 | Hull City | 29 | 7 | 8 | 14 | 30 | 38 | -8 | 29 |
| 20 | Stoke CityStoke | 29 | 6 | 11 | 12 | 26 | 36 | -10 | 29 |
| 21 | Portsmouth | 29 | 7 | 8 | 14 | 36 | 52 | -16 | 29 |
| 22 | Derby CountyDerby | 29 | 7 | 6 | 16 | 32 | 40 | -8 | 27 |
| 23 | Luton TownLuton | 29 | 7 | 5 | 17 | 29 | 48 | -19 | 26 |
| 24 | Plymouth ArgylePlymouth | 29 | 4 | 10 | 15 | 27 | 62 | -35 | 22 |
| > Championship Full Table | |||||||||
