When curricula change, teachers have to bring their knowledge and beliefs up to date. Two aspects can be distinguished: "what" do teachers learn and "how" is it learned. Two groups of teachers were involved during the preparation of a new chemistry curriculum. One group developed student learning material and subsequently enacted this in class. Another group only class-enacted this. Based on teacher learning, a model to understand teacher growth is presented. As the combination of a "development phase" with a "class enactment phase" proved instrumental, an existing model, the interconnected model of teacher professional growth, was extended. The consequence is that for teacher learning for a renewal a "(re)development phase" followed by a "class enactment" phase is essential.