Philosophy of science education can play a vital role in the preparation and professional development of science teachers. In order to fulfill this role a philosophy of science education should be made practical for teachers. First, multiple and inherently incomplete philosophies on the teacher and teaching on what, how and why should be integrated. In this paper we describe our philosophy of science education (ASSET approach) which is composed of bounded rationalism as a guideline for understanding teachers' practical reasoning, liberal education underlying the why of teaching, scientific perspectivism as guideline for the what and educational social constructivism as guiding choices about the how of science education. Integration of multiple philosophies into a coherent philosophy of science education is necessary but not sufficient to make it practical for teachers. Philosophies are still formulated at a too abstract level to guide teachers' practical reasoning. For this purpose, a heuristic model must be developed on an intermediate level of abstraction that will provide teachers with a bridge between these abstract ideas and their specific teaching situation. We have developed and validated such a heuristic model, the CLASS model in order to complement our ASSET approach. We illustrate how science teachers use the ASSET approach and the CLASS model to make choices about the what, the how and the why of science teaching.