Teachers: Do you give students afterschool detention?

My 12 yr. old stepsons math teacher gave him afterschool detention. She basically just sent a letter home Friday saying the he has afterschool detention Monday and to have him picked up at 3:45. We don't pick him up, he rides the bus to a neighbors house, because we don't get home any sooner than 6:00. This has made me and my husband furious. It seems like the teacher has no sympathy for working parents in handling detention this way. She should have spoken to us at the beginning of school and asked us if after school detention would be a problem for us. We have to both work to support our kids and it seems like the teacher just thinks that we should drop what we are doing, leave work and come to the school whenever she wants us to, and is not concerned with whether or not it is difficult for us or not. Do you do this with your students, and how should we calmly handle this?