One easy way for parents to begin making an impact in their child's education is simple: make school a priority at home. That might sound like a big deal but in reality it is quite an easy task. Simply make it a point to speak with your kids everyday about what is going on in their classes.
Ask them if they have homework, ask them if they have a test, ask them how things are going academically, etc. Don't take no for an answer. It might be awkward at first but eventually it will become an important and valued part of everyday. It doesn't need to be a grand dinner table conversation. A simple 30 second talk everyday can go a very long way towards making it obvious that you as a parent care about school.
Kids pick up on that. If you care, they will care. If you think it is important, they will think it is important. Even the most rebellious teenager who is trying everything to stay away from their parents will change their view on school if they know their parents think it is important. Its a very subtle thing but it makes a very large difference.