You aren't going to stop parents from holding back kids for kindergarten and in middle school. Yes lacrosse is one reason this happens but there are also other benefits to a given kid being held back; lack of maturity, academic struggles, etc. it's not always about lacrosse performance. The grade based system ship has sailed largely due to college recruiting practices. A better solution is limit the number of holdbacks a middle school club team can have (perhaps 4 per club team) and require birth certificates or state issued ID's for validation for leagues and tournaments.