Another good way to offset the negative influences at school is to involve your child in some kind of group that encourages, teaches, and praises moral, healthy behavior. In many cities, you don't have to belong to a church/religious body to have your kids attend the youth group or go to Sunday school.
It's a tremendously difficult to be a good parent and the primary provider. I will continue keep you, and other hardworking parents (single or not), in my prayers.
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