Teachers should be 'partners in learning' with parents, and 'leaders in learning' for students.
For example, my son was very slovenly about doing his maths homework. I found this out when he got a D for homework in his interim report. Son would tell me that he had no maths homework, he would then get a 20 min detention, which he wouldn't turn up to, then he would get an 1hr detention, which he wouldn't attend.
At parents evening, I asked the maths teacher if she would email me to let me know if he had handed in his homework, and give me the details of the exercise he was supposed to do. She agreed to do this, and unbeknownst to son, maths teacher and I conversed by email.
Son would come home - I would ask - "Have you got any maths homework", he would reply with bare-face lie "No", then I would reply, calm as anything, "I think you might be mistaken, you have Exercise 5c, questions 1, 2, and 5 on p. 35 to complete for Thursday", and he looked at me and said "How did you know?".
It took the maths teacher and myself to 3 months of emails (2-3 per week) to turn the situation around together. She and I were most definitely 'partners in learning', and my son's maths ability improved as a result.
Not every teacher is willing to chase up homework or converse with parents this way - in fact, she was the only teacher who was prepared to do this out of 4 subjects whom my son was then avoiding homework for. She is an absolute star of a teacher, and I wish there were more like her!