Which brand was most commonly used in West German schools? I know Commodore was big in Germany, which would make it a likely candidate, unless nationalistic pressure acted again?
There is no simple answer. Not so much due to any 'nationalistic pressure' (*1) but the fact that German schools are not run according to federal guidelines, but are managed on state level and in some cases on city level - plus some recognized independent bodies. All of them had different preferences, not to mention that early on not even the governing bodies gave out guidelines, so schools acquired a quite broad variety of machines.
During the 1960s and 70s a wide variety of Minis were bought by schools - in at least one case I know a /370ish mainframe and another Gymnasium owning a Zuse Z23. This includes many German machines like Walter, Dietz, TA, Kienzle or Nixdorf but as well DEC, IBM, Philips or other non-German machines. Usually the decisions were made at discretion of teachers and/or supportive parents. Of course, having a computer back then was only a thing in higher schools and only in more affluent areas.
When micros came along in the late 1970s, again schools often selected their own brand early on. These decisions were as well based on teacher/parent preferences, but as much influenced by local dealerships offering appealing deals. This was pretty much standard until state school governments did churn out guidelines and most importantly, bulk deals.
As one of the larger states, Bavaria is a great example. They did go for Commodore around 1980/81 making PET machines the default. But guidelines were open to support competition. The only other company besides Commodore having a larger share in Bavaria was Nuremberg based Triumph-Adler with their P series as well later on with PCs. Nonetheless, some state schools did continue to use other brands, or, like one Gymnasium in Munich, switched to Olivetti after the standard was set (*2). Or take Augsburg, were MAI machines were used.
During the mid 1980s, when the PC got established, a slow migration began - here IBM as well as SIEMENS and Olivetti managed to gather larger shares in Bavaria - beside, you guessed it, Commodore. Their PC 10/20 series were eventually the most used PC brand in Bavarian schools, despite SIEMENS PC being locally designed and manufactured in Augsburg. Still schools also vowed to use Atari ST as well. Heck, one trade school in Munich switched for C64 as late as 1984, at a time when PET or PC had been set for years.
The situation was like that all over Germany.
Bottom line: Next to any 1975-1985 home/personal computer could be found at German schools.
So yes, PET, Apple II, BBC Micro, Sharp, Triumph-Adler+, Olivetti, Philips, Atari or Amstrad were as well what German pupil saw first.
*1 - Commodore did argue toward officials that they were a German brand due to manufacturing in Germany, except IBM and Olivetti did the same :)
*2 - Which makes another nice case about the diverse structure of schools in Germany, as Munich is special in Bavaria by not being a state run school area, but city-run - and while state and city vowed for Commodore - and allocated funds - the school could still close their own deal.