Veronica,
Sounds like you have a tough group this year. Some parents have a hard time accepting the fact that they have failed and thus it is much easier to blame someone else for their short comings. Know that you are making a difference in the lives you touch each and every day. They may not show it at the moment by years from now they will realize they were blessed to be in your room. Treat yourself to a special outing, go shopping, ride your bike, enjoy dinner with a friend - simply get away from work for a few hours. Teaching is very rewarding and challenging but it can also suck the life out of you. Take care of yourself and know you are doing a wonderful job in your classroom. Hang in there!