This practical report explores the impact of forced learning design changes due to the Corona pandemic. At the School of Education Northwestern Switzerland over 2000 K-6 pre-service elementary school teachers got educated in computer science and computer science education over the last five years employing a learning design evolved through a Design Based Implementation Research (DBIR) approach. Assessing efficacy of the course through effect sizes the 2019 courses have served as pre-Corona baseline. Changing hastily in 2020 to online learning dramatically shifted the learning design in ways not initially anticipated in the DBIR process. Collaborative face-to-face (f2f) learning activities got replaced with individual online learning. Employing effect sizes has allowed us to quantify a Corona effect by comparing self-efficacy measures before Corona and during Corona. While there where only small effect sizes (0.5 > Cohen's d ≥ 0.2) all these small effects were positive suggesting that the individual/online seminar worked slightly better than the collaborative/f2f seminar. The report highlights the most important changes to the learning design and compares 2019 with 2020 using effect sizes. For the most part the report can only speculate about the most relevant factors in the design change resulting in the unexpected overall improvement of course efficacy. It could be the shift from collaborative to individual practices, the mandatory peer feedbacks, or the online learning situation.