This article describes a six-step approach used for the introduction of computer-supported laboratory exercises in Biology teaching. Following the model students will be guided from recognizing a problem question to the end report in a series of active tasks. The model was named APACER as an acronym of the six steps: Ask, Predict, Act, Comment, Evaluate and Report. The model was tested with 15 – 18-year-old secondary school students as group and individual work over a time span of ten years and several hundred students performing laboratory exercises in Biology. Work on development of the model can be described as reflective classroom practice. By observation of students’ work, grading of their reports and evaluation of results from exams, it was recognized that students achieved much higher grades because of better knowledge and improved reports. Transfer of the model to other Science subjects is suggested.