Every game is assigned a rank which is a measure of the level of difficulty for that game. G2 (U8) game is easier to do than a High School Rec game. So the G2 game has a lower rank than does the HS Rec game.

Similarly all referees have a rank which defines the assignor's perceived level of game that the referee is capable of working. 

New youth referees - with no game history - are assigned the easiest games to work.
      For THJSL these are as the Center (Solo) for the G2 (2nd Grade) games and as an Assistant Referee ("AR") for Grade 5 and Grade 6 games.

As the referee works more games and gains both experience and confidence the assignor will raise the referee's rank(s) so they can work higher level games.

When you log on to reftown, only games that you are qualified for will show up for you to self assign to.  

Turning Back Games
If you sign up for games and then turn them back you are NOT released from those games until the Referee Assignor takes you off those games. That means you can't take some other games - you are still locked into the first ones. So be careful if you're turning back one set of games in hopes of taking a different set. By the time the Referee Assignor gets you released from the first set, the new set might be already taken by another referee. If that happens, then you might be out of luck because someone else will have taken your original games!