Piaget's constructivist approach is of great benefit to teachers, and has indeed influenced the educational policy of many countries, most clearly the UK, through its focus on student centred discovery and emphasising the process of learning rather than simply the end product. The key contribution of Piaget is through Discovery learning, which is based on the belief that children learn best when they play, as it helps them through active methods to rediscover central "truths." In addition, Piaget's theory has been used to argue that children learn best when they have to work collaboratively so that they can learn from each other as they go through the experience of disequilibrium and try to make meaning together.
For me as a practitioner, Piaget's theory is so essential in many aspects. It explains why I do very little actual up-front teaching, and much more facilitation, because by being a facilitator I am able to use student-centred activities that force the learners to engage with the task at hand and make meaning themselves through active learning. For example, a Literature class I taught recently focused on the characters in Of Mice and Men and each group were given one character that they had to produce a spider diagram about, capturing their qualities, characteristics and physical appearance. They then had to return to the text and find quotes to support as many of these aspects as possible, which they then analysed, before producing a group essay. My role as a teacher was to circulate and support, modelling as necessary and helping individual groups, but it allowed learning to take place through active methods rather than simply me lecturing the class on characterisation in Steinbeck's classic. By producing their own spider diagram, learners learnt far more than if I had told them the same information.