While what you mention (capacity) is an absolutely important issue, I am skeptical of the effect that those 1-2 kids could have had on the students' performance

While what you mention (capacity) is an absolutely important issue, I am skeptical of the effect that those 1-2 kids could have had on the students' performance on a national level so suddenly. Immigration is not a new phenomenon here. I guess there could be more to it. Like, for example, Covid lockdowns, which were not implemented the same way (severity) for schools among European nations. That could also have had a big effect on students' performance, and even more on the performance of those 1-2 immigrant kids. What I am saying is the excuse that the authorities are giving is not convincing me TBH and the wording they choose makes me feel even more skeptical. My 2 cents.