Considerable research demonstrates this. It's not really a question of whether parent involvement is good, but why. It could be that involved parents are also providing better language environments at home. Or it could be that parents who are involved learn useful things about the school culture that help them prepare their children better. Parent-teacher involvement also can prevent miscommunications that could lead teachers to believe that parents aren't interested in their children's progress.
Parents get a more complete picture of what the children are doing.
When teachers meet the parents, they are often impressed with how interested the parents are, and by their capacity to actually help their children. This often leads teachers to raise their expectations about what parents can offer, and to develop mechanisms for parents to help. Teachers have to keep in mind that if they invite the parents to the school and the parents don't come, that doesn't mean the parents don't care. If I were a school principal, I'd make it the teach er's responsibility to meet the parents. Teachers also have to remember that in many cultures, parents give their children to the school, and they don't expect to have any say.