The Ipad2 reward system

There's no turning back our 4 yr old daughter is a gadget junkie. With kids nowadays who isn't?
It all started when this little 6 month old baby witness her mom & dad working from home...she had her own portable DVD for travel purposes then so on & so forth. With the Ipad2 we decided to make it a bit different and let her use it when she behaved well during the day. Strictly imposed no use rule if she misbehaved. So far it seems to be working for her so aside from the educational benefits - we try to make her read more complicated words beyond the CVC method & entertainment purpose it brings - she loooves playing games related to cooking & dressing up it helps that we get to use it to discipline her.