Problems at school

Please help! I have a spirited 5 year old, is a doll usually. lately
in school she has been in trouble. i have been getting notes from the
teacher saying she bit somebody, hit somebody or scratched somebody. I
talked to the teacher and asked her to
send me a note everyday as to how my daughter did in school. She
doesn't do that. She writes me a note only when my daughter  has hurt
somebody. On my part i remind my daughter everyday not to hurt others
and that she needs to talk and use words. I have given her time outs,
curtailed her TV and computer privileges, but i don't see an end to
this. She is apologetic and tells me i will never do it again, but
eventually goes back and does something like this again. These kind of
incidents have happened more often in the past one month. Last week
there was this biting incident and she has never ever done that before
and i was shocked to hear from her teacher that she did that. I am at
my wits end, i remind her everyday to keep her hands and feet to
herself.. what else can I do?? I don't want her to get into trouble!!
She's generally well behaved and talks well. I have tried behavior
charts, it helps for a couple of days and then the effect is gone...
can anybody share their experiences and help me??