For our family, given the choice between a nanny who minded our kids versus an educated, trained teacher who could engage our kids intellectually and emotionally, we chose the teachers every time. With their educational experience, and their understanding of the developmental needs of children, the teachers that we've employed have been ideal after-school companions for our two school-aged children.
I had the pleasure of hiring a Math teacher to work with my son who is challenged with Honors Geometry and other Honors Math curriculum. This teacher worked with my son once or twice weekly, and was so engaging and motivating that not only did my son learn these courses; he actually looked forward to their sessions.
Finding a mature sitter for my 4 kids was a nightmare until I discovered that a couple of the teachers at the school did babysitting. It was such a relief to know that my children were being looked after by an adult used to working with children. She met them at school, drove them home, supervised homework, and fed them. I never had to hire a teenager again!