Results of a research project in Vietnam together with findings from Western countries are presented in this contribution with special regard to the importance, challenges and perspectives in designing feedbacks for school stakeholders. Besides a longitudinal design using standardized tests to measure student growth in English, a video study was conducted in-between in 50 school lessons to acquire hundreds of indicators of classroom instruction. Right after the recorded lessons, teachers answered a short questionnaire about their own instruction. First, the results confirm previous findings that there is a universal problem of unreliable self‑reflection by teachers on their own teaching (T. Helmke et al., 2008). Without accurate self-reflection, teachers have no reliable basis for developing their teaching quality. Thus, professional programs are necessary to help teachers enhance their self-reflection accuracy. How such a system is being developed and applied will be mentioned using examples from Switzerland. Second, it is crucial to identify the most important among many instructional factors for student growth based on test results. However, test results can be variable depending on many factors including scaling model selection. The results point out significant differences regarding determinants of student growth depending on the scaling model. The uncertainty in results caused by the selection of a scaling model is often overlooked by researchers or policy-makers when reporting results and conducting secondary analyses (Ng & Koretz, 2015). This should be changed in the future. Using the model-averaging approach might be a possible solution for this problem (Robitzsch, 2016). Third, the nonlinear, compensatory and interactive joint effect of different instructional factors on student growth (Hasebrook, 2006; A. Helmke, 2014) was confirmed. The feedback should therefore focus on an appropriate balance of different factors and various forms of interaction rather than concentrating exclusively on or maximizing specific factors.

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